Last week was one of the strangest I've seen in electoral politics. It began with Barack Obama in danger of falling completely off a cliff, a danger that has only partially subsided. And yet it concluded with hints and suggestions by prominent Democrats and journalists that Hillary Clinton should just drop out of the race.

I'm trying to think of things to compare this to. Maybe the drawn-out and painful break-up of a relationship. You argue about this and that, the small things; she doesn't like that you watch too much football, you don't like the way she squeezes the toothpaste tube from the middle instead of the bottom, which any guy will tell you is the only logical way to do it. But eventually, the unavoidable must be discussed. All artifice falls away and you get to the point where one party or the other says, "Look, the bottom line here is ..."

We're reaching the bottom-line point. And the bottom line for what seems to be a majority of Democratic insiders is fear of a drawn-out and divisive nomination process. That argues for getting things settled sooner rather than later, and it means settling them in Obama's direction, since he's won more votes and delegates.

Democrats are highly jittery about the impact on the contest of Jeremiah Wright, the radical pastor whose anti-American rhetoric has taken parishioner Obama to that cliff's edge. The pre-Wright Obama was awfully close to being the perfect vote-for-him-and-feel-good-about-yourself candidate for white voters. The post-Wright Obama is a very different figure. As a friend of mine put it, it's as if white America suddenly discovered that Tiger Woods's best friend all these years was Malcolm X.

Numerous polls will arrive this week that show the impact of the Wright story. But, as of late last week, it appeared that Obama had stopped some of the bleeding with his big speech on race last Tuesday. If the coming polls suggest that that remains the case, then Democrats will be willing to take their chances with him, so to speak, Wright or wrong.

Prominent Democrats are saying so. Bill Richardson, an erstwhile presidential aspirant himself, endorsed Obama last Friday - a shattering blow to Clinton since Richardson had been a cabinet secretary in her husband's administration. The House speaker, Nancy Pelosi, without endorsing, has continued to indicate, even after Wright, that Obama is her preferred candidate.

And prominent pundits are saying so. Last Friday, just about an hour after the Richardson endorsement event, two top writers for the Politico, an influential website, posted a news article-cum-editorial arguing, accurately, that Clinton has almost no numerical case to make. Another uber-pundit and conventional-wisdom shaper, this one at Time, posted 14 reasons why Clinton should consider withdrawing. And so it was that the week that began with Obama on the ropes ended with Clinton being urged out of the ring.

I think it's too early for that, but only a little too early. Mark down May 7. That's the date by which Clinton should be one of two things: a, the possible nominee after all; or, b, out of the race.

Three important primaries will be held between now and then - Pennsylvania on April 22, and Indiana and North Carolina on May 6. The first of these is a state considered vital to the Democrats' chances in November. As for the other two, while no one really thinks John McCain will lose them in the fall, their Democratic electorates are so diverse that neither candidate can win them by simply appealing to his or her base voters.

Clinton's only remaining argument is to win all three of these states - and to win them big. If she can rack up three impressive victories in a row - and, crucially, if evidence from exit polls suggests that the Wright story cost Obama hefty percentages of white voters - then and only then can she go to her fellow Democrats and say: Look, he's tanking. We just can't send this guy out to represent us in the fall.

Any outcome short of that makes Obama the nominee, I would think. It doesn't really matter what it is. She wins Pennsylvania by 10 points, and they split the other two in fairly close votes, for example; for Clinton, not enough. In any case like that, it will be apparent that Clinton cannot catch Obama either in the total popular vote (which Obama leads by 700,000 right now) or the pledged delegate count (which he leads by around 140).

So if we wake up on May 7 and Clinton doesn't have clear momentum, and the evidence that the Wright association will badly damage Obama in November is anything less than manifest, I'd expect that the calls will mount for her to come to terms with the numerical reality and end her campaign.

Whether she'll respond to them is another question. Her campaign has given every indication that it will stay active throughout the primary season, which ends on June 3. She'll hope that she's close enough to muddy things up.

But what happened last week is that Democrats began to signal that what they want is clarity. After 16 rollicking years, they're breaking up with the Clintons. Like I said, the unavoidable must eventually be discussed.

michael.tomasky@theguardian.com