With big wins in Ohio and Texas last night, Hillary Clinton has finally broken her losing streak and sent a clear message to Barack Obama: I'm not getting out.
For the Illinois senator, the meaning of the primaries is clear - he has to get tough. Hillary can still win this nomination. The proportional representation system of allocating delegates chosen by primaries and caucuses mutes the impact of the popular vote.
By the time the Texas caucuses are fully counted, Obama may have maintained or even expanded his delegate lead, despite Hillary's victories in three out of four states.
Among the remaining 600 delegates to be chosen, Obama should be able to add to his lead.
But there remain 800 superdelegates, each entitled to a full v ote. No matter if Obama leads among elected delegates, they can still deliver the nomination to Hillary.
Do they dare?
If Clinton is able to score a series of popular-vote victories in these late primaries, she could lay the basis for an appeal to the superdelegates to disregard the results of January and February and look instead at her success in the later contests.
The battle of Hillary is over. The battle of Obama has begun.
The question of his readiness and experience looms ever larger in the minds of the media and of voters.
Her red-phone ad, citing her supposedly superior readiness to be commander in chief, evidently cut deeply among the electorate.
It's time that Obama counters her strategy by hitting back. His lofty politics of hope will avail him little in the aggressive, rough-and-tumble world of modern politics.
He's got to spell out the special-interest connections that stigmatize Hillary as the tool of the lobbyists.
He must underscore the need for her to release her tax returns for 2007 and 2006 to show the source of her new-found wealth.
He's got to learn to trade blows with the Clintons, the best counterpunchers in the business.
Looming above the primaries is the specter of the unseated delegations from Michigan - chosen in a primary with only Hillary's name on the ballot - and Florida.
Obama needs to stop her gathering momentum by shedding his ingenue status and fighting hard for the nomination his previous victories have earned him.