On a summer’s eve three years ago, I received an e-mail message from a friend of mine. It went something like this: “I’m at La Loma. On the night he kills immigration reform, Mitch McConnell is eating Mexican for dinner with his wife.”

Now, Capitol Hill denizens know that McConnell, the Senate Minority Leader, and his wife, former Labor Secretary Elaine Chao, are regulars at La Loma, the popular eatery with the killer margaritas on Massachusetts Avenue Northeast. So the fact that he was there on the June night in 2007 when Senate Republicans, despite pressure from the Bush White House, decided to cast aside consideration of an immigration reform bill was probably just coincidence.

But the image was seared into the brain of my friend, who happens to be a top Hispanic Democratic operative. And it was certainly ironic, to say the least.

Well, today, the Kentucky Republican is preparing to eat crow. Perhaps this will bring my friend — and thousands of other Americans who have long feared or hated Mitch McConnell — some satisfaction.

In fact, though this is looking to be a very bad election cycle for Democrats, they may get a few cheers out of tonight’s primary results. For not only will we get to watch McConnell’s discomfort as Rand Paul, rather than McConnell’s hand-picked candidate, Kentucky Secretary of State Trey Grayson, wins the Republican Senate nomination in the Bluegrass State. We also may get to watch Sen. Arlen Specter’s long political career come to an end — or at the very least, we’ll get to watch him squirm a lot.

I know, I know — Specter, a year after his party switch, is the Democratic establishment candidate now. Barack Obama says he loves him, calls into a meeting of African-American ministers in Philadelphia the other day, saying how much he needs him in Washington. The political machine of Democratic Gov. Ed Rendell may have just enough juice left to save Specter in his primary with upstart Rep. Joe Sestak — whom, frankly, no one likes.

But come on: Won’t most Democrats secretly be cheering if Specter takes it on the chin?

Let’s accept, at face value, Specter’s claim that, rather than worrying about his political hide, he concluded that he could no longer function in the Republican Party — the old saw about not leaving the party but the party leaving him. It’s got to be unbearable to be a Republican moderate in Congress these days — except on those rare occasions when GOP leaders trot you out to prove what a big tent they’ve got.

And yes, through his long Senate career, Specter did break with his party on some key votes, particularly on social issues. But this is the guy who eviscerated Anita Hill. Who voted against Elena Kagan just last year to be solicitor general — a functionary’s job. Who not only voted for, but fought for, Samuel Alito to be on the Supreme Court. Who sought and required the blessing of George W. Bush to limp through the Republican primary six years ago.

Sestak may or may not be a stronger candidate for Democrats than Specter in November. He may be every bit the unpleasant character that “Snarlin’ Arlen” has been over the decades. There may prove to be some fire to the smoke that Republicans are peddling, about the White House offering Sestak an administration job to drop out of the Senate primary.

No matter. It’s hard to imagine many Democrats shedding a tear if Specter is rendered a lame duck tonight. And the Wednesday morning quarterbacking over whether he killed his political career with his party switch will be breathtaking. But that’s the would-be party switcher’s dilemma: It’s hard to be competitive in a primary no matter which one you enter.

As for McConnell — well, the temptation is to say it couldn’t happen to a nicer guy (though he probably last smiled in 1957). This is someone who has ruled the Kentucky GOP with an iron fist for years, mostly with great success (though one-term Gov. Ernie Fletcher turned out to be something of a dud). Now, in Paul, McConnell faces the prospect of having to support a nominee who hasn’t even committed to supporting him for Republican leader next year.

The whole Ron Paul phenomenon, which the younger Paul has become a part of, remains hard to read, because as it evolves it has simultaneously become of and apart from the broader tea party movement. Rand Paul is the first real acolyte of Rep. Ron Paul (R-Texas) to enjoy real electoral success. And it’s clear that a Sen. Rand Paul would give Mitch McConnell fits.

But will there be a Sen. Rand Paul? Optimistic Democrats seem to think that a Paul victory in the primary increases the chances that they can steal the Kentucky seat in November. Another reason for Democrats to cheer tonight?

Go ahead and cheer if you want to, Democrats. But don’t bet on Paul losing.

Even though state Attorney General Jack Conway appears headed to victory in today’s Democratic Senate primary — he’s got the momentum, at any rate — and even though he’s a skillful, attractive politician with an All-American look, this is Kentucky, after all, a state that gave Sen. John McCain (R-Ariz.) a 16-point victory in 2008 and has probably lurched considerably more to the right since then. The Democrats’ only hope for victory there in November is for Paul to do something crazy.

Other than allowing himself to be photographed the other day in garish-looking shorts while wearing a sports jacket and tie, Paul hasn’t really done anything crazy yet — and it’s hard to imagine what would constitute crazy to an angry Kentucky electorate that, in making Rand Paul a Senator, can simultaneously punish both Mitch McConnell and Barack Obama.