Clinton's inevitability raises question: What's next for Bernie?

The Democratic nomination Tuesday night became Hillary Clinton's to lose – and her commanding wins in Maryland, Pennsylvania and Delaware mean there is almost no way she can fail in her second, grueling quest to be the first female major party presidential nominee.

Speaking in Philadelphia, the city where Clinton would be officially crowned the nominee, the former secretary of state talked like a general election candidate, slamming the GOP for what she called divisive and negative rhetoric.

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"We will unify our party to win this election and build an America where we all rise together, an America where we lift each other up instead of tearing each other down," a beaming Clinton told cheering supporters.

She made merely a passing criticism of her opponent, Sen. Bernie Sanders of Vermont, whom she has characterized as long on pie-in-the-sky rhetoric and short on plans. "We have to be both dreamers and doers," Clinton said.

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Sanders won the nation's smallest state, Rhode Island, in a victory that served as a metaphor for a candidate who has done far better than expected but still always lagged behind the front-runner.

Clinton's win makes it all but mathematically impossible for Sanders to catch up, especially with Clinton's dominance among the "superdelegates," elected officials and party bigwigs who get a say in selecting the nominee at the convention. But Sanders has shown no indication he will drop out of the race, a move that would allow Clinton to focus on the general election but take the once-relatively unknown Vermont lawmaker out of the national spotlight.

Sanders' campaign has made noises about convincing superdelegates to switch sides once the nomination comes to a vote in Philadelphia in July. But that possibility seems even more dim with Clinton's performance Tuesday night. Aside from winning lopsided victories in three states, Clinton dominated among women and African-Americans, both critical Democratic constituencies.

Senate Democratic Leader Harry Reid of Nevada acknowledged Sanders' fate Tuesday afternoon, saying he didn't see how Sanders could get the nomination. The Capitol Hill veteran "has run a campaign that I think we've all recognized has been unique and powerful, and I think Bernie should do what he wants to do," Reid told reporters, declining to call on Sanders to leave the race. Asked directly if he thinks Sanders could still win the nomination, Reid said, "No, I do not."

Sanders campaigned Tuesday night in West Virginia, calling his supporters "revolutionaries" committed to "transforming our nation." While his campaign manager, Tad Devine, told news organizations Tuesday that Sanders would reassess his campaign on Wednesday, he gave no indication Sanders would actually give up the fight.

Many observers believe Sanders will stay in the race until the convention, if not to seriously challenge Clinton, then to satisfy the supporters who made the improbable contender a serious challenger to a powerful former first lady, U.S. senator and secretary of state. Sanders has railed against big money in politics – mainly against large donations from special interests – yet has displayed a remarkable ability to raise tens of millions of dollars a month in donations as small as $2.70. As long as he has cash, analysts note, there's no pressing reason for him to step aside.

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And when tens of thousands shout out "Feel the Bern!" at his rallies, it's easy for Sanders to believe it's possible to wrest the nomination, notes Garrison Nelson, a University of Vermont professor and longtime watcher of Sanders' political career.

"Bernie's didactic. That's his problem. He's a sermonizer. That's his strength, and that's his weakness," Nelson says. He's gotten so hooked on his applause lines." That makes it harder, analysts say, for Sanders to reconcile the enthusiasm at his massive rallies with his lagging performance in the delegate race.

"I think it was sort of surprising how much traction he got as the race went on. He expected to be sort of a gadfly, not someone who actually had a chance," says Seth McKee, a political science professor at Texas Tech University. "I think there were months in the campaign where he actually thought he had a chance to win. He got closer than he thought he would."

But the enthusiasm for Sanders has turned out to be no match for the strategic work of an experienced Clinton campaign, which started early in wooing superdelegates and local political and civic leaders. Clinton eschewed the huge rallies and instead has done smaller events aimed at targeted audiences.

That plan was rewarded with a 16-point victory for Clinton in New York, a primary Nelson sees as the turning point for the Sanders campaign. While Sanders was rallying a crowd of 28,000 in Brooklyn, Clinton was addressing a small crowd on mostly-Republican Staten Island, listing her accomplishments as senator from New York. She ended up taking Staten Island – along with Sanders' home borough of Brooklyn.

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The Vermont lawmaker was also damaged, Nelson notes, by an interview he gave to the New York Daily News editorial board in which Sanders appeared to have an unformed foreign policy and no specific plan to break up the big banks, as he repeatedly has pledged to do.

Pennsylvania and Maryland were challenging for Sanders from the start, as both have traditional Democratic constituencies, such as African-Americans in both states and an older electorate in the Keystone State, that have favored Clinton in primaries so far.

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The question Democrats have is: What does Sanders want? And how will he conduct himself for the remainder of the campaign?

Sanders has said he wants to shape the party's message and platform, meaning in practical terms that he would be given a speaking role at the convention. That might be hard for Democrats to swallow if Sanders continues to criticize Clinton aggressively. Her camp is particularly irritated with Sanders' charges that Clinton is getting around campaign finance rules, since it feeds Republican Donald Trump's "Crooked Hillary" line of attack.

Clinton would need Sanders supporters to embrace her – or at least vote for her – in November, and that would require Sanders to endorse Clinton formally. Since Sanders was not even a Democrat until he sought the party's nomination for president, he has no established ties or loyalty to the party, notes Nelson, who adds that Sanders ran against Democrats on 10 occasions in his career.

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But if he refuses to endorse Clinton – who not only endorsed President Barack Obama but urged delegates to nominate Obama by acclamation despite having endured a bitter 2008 primary campaign against him – he will likely be denied a formal role in Philadelphia, Nelson predicts. California Gov. Jerry Brown, who ran for president in 1992, was refused a convention speaking role in New York City that year because he declined to endorse Bill Clinton.

"You can be damn sure the Clintons will impose the same on Bernie if he chooses not to endorse her," Nelson says.