Voters in Texas and Ohio, as they did in New Hampshire, have halted Barack Obama's headlong surge toward the Democratic presidential nomination and sent a signal that the race should go on.
But despite Hillary Clinton's exuberant declaration that "as Ohio goes, so goes the nation," it remains unclear if her victories Tuesday in these bitterly fought primaries will provide the crucial momentum to overcome Obama's lead - or represent only the late-primary buyer's remorse we've seen in past campaigns.
Such primary victories by seemingly beaten candidates in the 1970s and 1980s failed to block Jimmy Carter, Ronald Reagan, Gerald Ford or Walter Mondale from their party's nominations.
Clinton may win, at best, fewer than 20 more delegates from Tuesday's four primary states, so despite popular vote triumphs in three of them, she still faces an uphill fight to overcome Mr. Obama's lead among the delegates who will decide the nomination.
Indeed, that lead is likely to grow before the Democratic race reaches what she wants to make the next major showdown: April 22 in Pennsylvania. He'll be favored to expand his lead Saturday in the Wyoming caucuses and next Tuesday in the Mississippi primary.
On the other hand, Clinton's successes and the way she achieved them have punctured the myth of Obama's seeming invincibility created by his streak of 12 primary or caucus victories.
In the process, she also underscored the kinds of doubts about the Illinois senator that Republican John McCain might be able to exploit in the general election.
In Texas, two-thirds of late-deciders voted for Clinton, according to network exit polls. A key factor may have been her television ad that featured a ringing red phone and questioned his experience to handle a sudden, unexpected international crisis.
In Ohio, her success in exploiting the state's economic misfortunes - and Obama's uncertain response to questions about his motivation in attacking her on NAFTA - renewed another question: whether he is tough and experienced enough to fight what Democrats call "the relentless Republican attack machine."
The Ohio results also revealed a potential problem for Obama if he wins the nomination, notably the erosion of the white support that was a major factor in his primary triumphs in such states as Wisconsin and Virginia.
Exit polls tell us that Clinton defeated Obama by more than 15 percent among white men, compared with his 30-point victory among that group in Wisconsin. She also expanded her support in the party's traditional base by winning a majority of voters with family incomes up to $100,000 and doing well among those with less education.
That's important because Ohio, unlike Texas, seems likely to be a major battleground state in the general election.
And while most voters said neither race nor gender was an important issue, among those who did, some 60 percent voted for Clinton. Just last week, a Pew poll showed that one in five white Democrats said they would vote for McCain if Obama were the Democratic nominee, twice as many as said they would defect if Clinton were chosen.
All this suggests that Clinton's aggressive campaign in the last two weeks and greater media scrutiny of Obama have combined to dim his positive image.
At the same time, Clinton's deficit in the delegate fight suggests she still faces an uphill battle to win the nomination. The next few weeks may show if she can slow or reverse a recent slow drift of superdelegates to Obama.
If that drift continues, it would indicate the party establishment recognizes that, despite Clinton's strong showing Tuesday, Obama remains the likeliest nominee and wants the race to end sooner, rather than later.
If it slows, it would signify growing doubt that he would be as strong a candidate as he may have seemed. Most recent polls still show him running better against McCain than Clinton would.
In any case, Tuesday's results eliminated any immediate reason for her to abandon the race. She raised millions in February and can rightly claim that her message - that she would be best prepared to serve as commander in chief and take on McCain - is getting through.
The seven weeks until Pennsylvania may be a long time for her to sustain Tuesday's bounce. But it also provides more time to scrutinize Obama's qualifications and proves again the value of an extended campaign.