Thirty years ago this week, more than 100 million Americans tuned in for the first airing of “The Day After” on ABC — the audience eager, during the final years of the Cold War, for a blockbuster vision of what the heartland might look like if both Washington and Moscow exercised their nuclear options.

On the day after the biggest change to the congressional rules in four decades — sharply curtailing the power of the filibuster, an essential element of life in the Senate — the public may be clamoring for some insight into what just happened.

These six questions and answers may help.

1. Why is it called the “nuclear option”?

The allusion to an atomic blast is as much about how the Senate rules were changed as about the way in which the rules were changed.

The breadth of the impact on the legislative process, and on the balance of power at the Capitol, is undeniably significant, although its extent cannot be precisely measured just now. The number of political players who have seen their power hobbled by the move is also extensive, but can’t yet be quantified.

In those ways, the situation is analogous to the detonating of a nuclear bomb: Plenty of the damage is plain to see, but the breadth of the fallout takes a long time to measure. For now, it’s only clear that the minority’s right to filibuster most judicial and all executive branch nominees has effectively been destroyed, and that means the Republicans are the only victims. But there is nothing to prevent efforts to end the legislative filibuster from bubbling up soon enough. And it’s a dead certainty that whenever the Republicans win control of the Senate, whether next fall or in an election years later, they will turn the tables on the newly-entrenched-in-the-minority Democrats with a vengeance.

The way in which Majority Leader Harry Reid, D-Nev., deployed his power play on Thursday also had some similarities to the start of a nuclear war. Like many missile attacks, his series of choreographed parliamentary moves and roll call votes had been threatened for a long time, was stealthy in the planning, undisguised in the execution and swift to reach completion. And it was impossible to contain the damage once the launch sequence was begun.
2. How did it come to this?

The change is the most fundamental alteration to the way the Senate functions since 1975, when the supermajority required to break a filibuster, known more formally as invoking cloture, was reduced to 60 from 67.

For the next three decades, meeting that three-fifths-of-all-senators threshold was relatively rarely required for overcoming either ideological objections, or dilatory protests, in order to advance legislation or nominees. But the situation devolved quickly in 2005, when a Republican majority sought to confirm a series of President George W. Bush’s judicial picks and were thwarted by a unified Democratic bloc, which labeled the nominees too conservative for confirmation. Majority Leader Bill Frist, R-Tenn., came within as a day of trying a maneuver similar to what Reid executed Thursday, but pulled back after seven senators from each party – the “gang of 14″ — announced they would begin opposing filibusters of judicial nominees except in “extraordinary circumstances,” a phrase left undefined.

That eased tensions a bit through the end of the Bush years. But, soon after President Barack Obama took office with fellow Democrats running the Senate, the filibustering of nominees spiked to unprecedented levels. The official numbers from the Senate confirm a principal talking point of Reid’s – that half of all the filibusters to thwart confirmations in the history of the Senate have come during this administration.

3. Why did this happen when it did ?

After a couple of bipartisan compromises on the margins of the debate failed to do much to change the situation, Reid came under increasing pressure this year from the junior members of his own ranks, who have now come to dominate the Democratic caucus. Thirty-three of its 55 members have arrived since 2007, meaning they have been in the majority their entire Senate careers and have never needed or experienced the benefits of the main Senate rule created to preserve power for the minority party.

Only in the past week, though, did Reid become confident he had sufficient votes to prevail in the parliamentary showdown; the tipping point seemed to come when veteran California Democrat Dianne Feinstein announced she was reversing her position and would support the nuclear option.

Beyond that, Reid looks to have concluded he had very little to lose in the short-term, and some not-unimportant benefits to gain. Essentially nothing substantive that his caucus or the president might propose looked to stand a chance of getting past a Senate GOP wall of resistance before the midterm elections anyway, so from his point of view, the post-nuclear-option outrage from the Republicans could not translate into any more obstructionism than was already taking place.

And, while the legislative system may remain totally locked up for as long as three years, Reid and the Democrats have gained virtually unfettered power for at least one more year to deliver to the president the people he wants to manage the executive branch and advance his regulatory priorities – a power made all the more important at a time when few new laws are being written

At least as importantly, the change means that, at least until the midterms, Obama will be able to fill as many circuit court of appeals and district court vacancies as exist with lifetime appointments, an opportunity to assure his vision for interpreting the law long outlasts his time in the White House.

Democrats had become confident that Republicans were preparing to “go nuclear” at their first opportunity, and it’s probably an even-money bet that could be in January 2015. So they concluded they were willing to take the blame for an institutional explosion that was inevitable anyway, because at least they would be able to reap the benefits for a year

In the interim, Reid is hoping the public takes little interest in the insiders’ complaints about “breaking the rules in order to change the rules,” as Minority Leader Mitch McConnell, R-Ky., fairly described the move, and more about the chance of restoring some semblance of functionality to the place: “It’s time to change the Senate before this institution becomes obsolete.”

4. How angry are the Republicans?

They certainly sound hopping mad — especially because they view Reid as having patently broken a promise, reiterated as recently as July, not to do what he just did. In these dysfunctional times, the reliability of a Senate leader’s word had been one of the few filaments of trust that kept the place operating at all.

To vent their disapproval, Republicans mounted a filibuster that prevented the Senate from finishing deliberations on the annual defense authorization bill this week — although a lopsided GOP majority wants the measure enacted, just as it has been 52 years running. The two-week recess bracketing Thanksgiving will in theory give the GOP time to get beyond its feelings of betrayal. If the Senate returns with even the normally collaborate Republicans intent on tying the place in as many parliamentary knots as possible — and plenty of dilatory maneuvers remain available even without as many filibuster openings — that will mean the cooling off period didn’t work.

Nonetheless, such public fury from the Republicans in the short term might be masking a little bit of relief that the Democrats have done some of the long-term dirty work for them.

There’s little reason to doubt that McConnell was ready to curb the power of the filibuster were he to become majority leader – especially if a Republican wins the presidency in 2016 and the GOP holds the House, giving the party control of all the policymaking levers for the first time in a decade. Reid’s move means McConnell won’t have to press the initial detonation button, and probably wouldn’t take all that much criticism if he moves to eliminate the legislative filibuster as well in order to advance his party’s agenda.

5. Why didn’t Democrats eliminate filibusters on legislation?

There is nothing, procedurally, to prevent them from doing so. As Thursday’s developments show, changes in the Senate rules, which are supposed to be fully debatable and subject to a two-thirds-majority vote, can effectively be changed by a simple majority.

But there does not appear to be any move afoot by the Democrats to take the next logical step by ending the filibuster altogether. The main reason is that they would reap no benefit from dropping that second nuclear bomb. Because nominations aren’t handled by the House, the new rules give the Democrats uncheckable ability to give their president what he asks for. Not so with legislation, which of course has to be passed in identical form by both the House and Senate to become law. Democrats have nothing to gain by streamlining the system so their bills can get more quickly across the Capitol, because the current House GOP majority would still be likely to shelve the measures in opposition to the policy changes being proposed.

But, to drive the point home, Speaker John A. Boehner, R-Ohio, has declared that he House would not touch a bill, no matter its merits, if it had been passed by the Senate without having to run the current cloture-first gantlet.

6. Why the exception for Supreme Court nominees?

Democrats were willing to accept that someday a Republican Senate will be able to quickly fill lower-court vacancies with the super-conservative nominees from a GOP president. But they were unable to acquiesce in that same scenario for the highest court in the country — especially at a time when its ideological balance is on a knife’s edge, and when advocates for abortion rights and other liberal causes were expressing wariness of the risk.

The tradeoff is that, by preserving the filibuster as a tool to stop Supreme Court nominees, Reid has made it potentially significantly difficult for Obama to install a new justice for the rest of his presidency. Especially if an opening unexpectedly occurs soon, while the pain of nuclear winter is still palpable, Republicans would be very tempted to unite against anyone Obama might choose — even if that meant leaving one of the court’s nine seats empty for a time.

Of the two liberal anchors of the court, Ruth Bader Ginsburg would be 83 at the time of the next presidential election, and Stephen G. Breyer 78. Both Anthony M. Kennedy, the only genuine swing vote, and Antonin Scalia, the leader of the conservative bloc, will turn 80 in 2016.