Imagine, if you will, a parallel universe.

Imagine, instead of health care reform being the raging topic of public discourse right now, that the war in Iraq had just started.

[IMGCAP(1)]Imagine the Republicans and not the Democrats in full control of Congress and the White House.

Now imagine a man flying a plane into a government office building in Austin, Texas, not to protest the Internal Revenue Service, but to protest the war. Imagine a liberal Congressman, rather than conservative Rep. Steve King (R-Iowa), saying he empathized with the pilot, even though an innocent man died in the crash.

Imagine another liberal Congressman standing before a crowd outside the Capitol, as Rep. Michele Bachmann (R-Minn.) did recently, suggesting that patriotic Americans refrain from paying their taxes to protest government policies. Imagine a prospective Democratic presidential contender saying, as Minnesota Gov. Tim Pawlenty (R) did during his Conservative Political Action Conference speech last month, that it’s time to “take a 9-iron and smash the window out of” the federal government. Imagine another potential Democratic presidential candidate highlighting on her Web site the districts of Members of Congress she wants her supporters to defeat in a rifle scope, as Sarah Palin (R) did last week.

Finally, imagine Democratic Members of Congress standing on the Speaker’s Lobby balcony encouraging angry protesters down below. Imagine Democratic Members in the House chamber shouting at the president, or calling a colleague a “baby killer.”

Imagine all these things and think of the political consequences for the Democrats.

The Democratic Congressman applauding the IRS bomber would be accused of fomenting terrorism. The Democratic equivalents to Bachmann and Pawlenty would be called treasonous. The others would be accused of inciting violence. Conservative talk radio hosts would be calling for their arrest. Republican House Members would be drafting resolutions to censure their colleagues — and maybe even to expel them.

This is not an episode of “The Twilight Zone.” It’s a perfectly plausible scenario.

Have we heard anything remotely like that level of condemnation from Democrats in the past few weeks? Or from left-leaning commentators? No.

Anyone still believe in the myth of the all-powerful liberal media?

Polls and conventional wisdom suggest the Democrats are enjoying a short-term bounce now that health care reform has passed. President Barack Obama received a hero’s welcome in Iowa City on Thursday, and he and other Democrats will be doing all they can over the next several weeks to convince voters of the benefits of the legislation. Republicans will be out on the hustings also, trying to remind people of how expensive health care reform is and how it could be a very real drag on the already-slow economic recovery.

But the GOP spin for now is being drowned out by Republican bad behavior — by the heat of Members’ rhetoric on Obama and health care and the frenzied reaction it seems to have whipped up among certain conservative activists. No doubt the public’s revulsion to the scene of angry mobs and reports of threats against Democrats has as much to do with the small uptick in support for the reform plan as the substance of the legislation itself.

But that’s just a happy coincidence for Democrats — most of whom left health reform for dead until a couple of weeks ago. Among party leaders and their supporters in the media, there has been in recent days some scolding of Republicans, some head-shaking, some finger-pointing, some calls for decorum, even some demands for GOP apologies. But no one has accused Steve King of aiding and abetting domestic terrorists. No one has questioned Michele Bachmann’s patriotism. No one has accused Tim Pawlenty of treason. Heck, House Majority Leader Steny Hoyer (D-Md.) even found time last week to apologize — for calling anti-health-care-reform protesters “un-American” in a USA Today column he wrote last summer.

What we are witnessing here is the essential difference between the two political parties. Sure, the Democrats have their blowhards and knuckleheads, and sure, passions on the left sometimes devolve into out-of-control fury. But it is not the custom of Democratic officeholders to call their critics unpatriotic — a Republican tactic that’s so commonplace we hardly even notice it anymore. It is not the custom of Democratic lawmakers to question the legitimacy of a Republican president, as some GOP Members of Congress continue to do with Obama by aligning themselves with the odious “birthers.” Democrats did not do this even when the last Republican president, George W. Bush, lost the popular vote in 2000. In fact, many Democratic Members rushed to embrace his agenda.

And it’s not the custom of Democratic politicians to rile up their base in the same visceral way that Republican lawmakers did on the Capitol balcony last week. If anything — as many leaders of Democratic-aligned interest groups will glumly tell you — the Democrats often run away from their base, worried about the political consequences of being perceived as too-far left, while Republicans usually head straight to theirs.

In recent days, Republican Congressional leaders have repeated like a mantra that there has been anger and passion “on both sides.” And longtime political observers will disagree about where all the partisan rancor first came from. The Robert Bork hearings? The Clarence Thomas hearings? The Richard Nixon impeachment? The Bill Clinton impeachment?

That question is immaterial for the moment. The electoral consequences of all this divisiveness, this November and beyond, is impossible to calculate. But one thing is clear: When it comes to all-out, burn-your-ideological-opponent-at-the-stake politics, Republicans are the sole practitioners. And why not? It has usually served them well.