Just about everyone, including Barack Obama, agrees these last few weeks have been tough ones.
He missed a chance to close out the Democratic presidential nominating fight by losing Ohio to rival Hillary Rodham Clinton, then lost again in Pennsylvania. His big lead over Clinton in national polls disappeared.
Worse, the Rev. Jeremiah A. Wright Jr. -- Obama's longtime pastor -- resurfaced, spitting fire during a National Press Club appearance. The Illinois senator was badly burned in the process.
Yet for all that, Obama remains a strong favorite to win the nomination. The simple reason is mathematics: His lead among elected delegates makes it virtually impossible for Clinton to win without having the nomination handed to her by party insiders, the so-called superdelegates.
"We have demographic gridlock, and we have rules that make it very difficult to catch up when you're behind," said Bill Carrick, a neutral Democratic strategist, referring to the candidates' distinct appeal to separate constituencies and the proportional way Democrats award their delegates. "It all conspires to make a very rigid, inflexible process."
Which does not mean the contest is likely to end soon.
The next test comes Tuesday, when Indiana and North Carolina hold their primaries. Barring the unexpected -- a blowout in either state, or twin victories by either Obama or Clinton -- the probable outcome is a continued stalemate.
That would give each candidate incentive to keep running at least until June 3, the last day of the primary season: Obama because of his seemingly insurmountable lead in nominating delegates and the popular vote, and Clinton because of doubts sown in recent weeks about Obama's general-election viability.
"As long as he wins where he's supposed to win, and she wins where she's supposed to win, the nature of the race is fundamentally unchanged," said Ben Tulchin, a Democratic pollster watching the race from the sidelines. "And so it continues."
But as the election season grinds toward a close, the pressure on Clinton to change the dynamic of the contest has grown more pronounced. Nearly 90% of the pledged delegates have been chosen. Even if she wins all the remaining primaries in a landslide, the New York senator would still need to corral an overwhelming proportion of the party's undeclared superdelegates -- the party leaders and others with an automatic vote at the Democratic convention -- to seize the nomination.
The latest count by the Associated Press showed Obama with 1742.5 delegates to Clinton's 1,607.5. It takes 2,024 delegates to clinch the nomination at the Democratic National Convention in August. Among superdelegates, Clinton's once-dominant lead has been winnowed to less than two dozen.
There is little reason, however, for the former first lady to quit, as long as she continues to win and Obama struggles, as he has since his allegiance to the incendiary Wright became an issue.
The senator broke with his ex-pastor after Monday's National Press Club speech, but Clinton supporters cited the episode as justification for her continued candidacy.
"It raised the question of experience," said Jerome W. Mondesire, president of the Philadelphia NAACP and a pledged Clinton delegate. If Obama cannot handle a "whack-a-doodle like Wright, how is he going to handle a crazy head of a government with a nuclear weapon?" Mondesire asked. "That's far more dangerous than a Jeremiah Wright."
But the controversy may have helped Obama to a degree. If his nomination is inevitable, the thinking seems to go, better to end the fight before too much more damage is done. That may explain the latest batch of superdelegates who have jumped off the fence to support Obama.
"I'm concerned about this thing being dragged out," said Rep. Baron P. Hill, the congressman here in Bloomington who endorsed Obama on Wednesday. "The more people like myself who come out, hopefully that will help the process along in terms of bringing closure."
For all the gyrations -- about Wright, about whether people in small towns are "bitter," about Clinton's erroneous claim that she came under sniper fire in Bosnia -- voters have scarcely wavered in their sentiments. The results have been dictated more by states' demographic makeup than any swings in loyalty.
Obama has consistently claimed the allegiance of young voters, African Americans and voters who are better educated and wealthier. Clinton has equally strong backing from women, less-educated voters and the economically hard-pressed. In states where Obama's demographic groups hold sway, he wins. Where Clinton's do, she wins.
If the pattern holds, that makes Obama the favorite to win North Carolina and gives Clinton the edge in Indiana.
The two campaigned across the states Saturday -- Obama in Indiana, Clinton in North Carolina and later Indiana -- continuing their squabble over a proposed federal gas tax "holiday."
Both have aired TV ads criticizing each other's position on a temporary suspension of the 18.4-cent-a-gallon levy. Clinton favors eliminating the tax over the summer to give motorists some relief at the pump; Obama decries the plan as a stunt that will yield little benefit to consumers.
On Saturday, Obama portrayed his stance as a matter of principle, suggesting Clinton was merely chasing votes.
Speaking to an audience at an Indianapolis high school, Obama said the proposal, also backed by the presumed Republican presidential nominee, John McCain, would save motorists the equivalent of half a tank of gas, if that.
"So this is not about getting you through the summer, it's about getting elected," he said. "And this is what passes for leadership in Washington -- phony ideas, calculated to win elections instead of actually solving problems."
Clinton gave no quarter, even taking on a protester who criticized her proposal at a stop in Gastonia, N.C. "I see that sign over there," she said. "A guy's got a sign saying a gas tax holiday is blatant pandering. Well, I'd rather the oil companies pay the gas tax than you pay the gas tax this summer."
For all the candidates' exertions, election returns and opinion polls now matter only to the extent they influence the true decision-makers: the superdelegates.
Unless there is a runaway winner in the final stages of the primary season, superdelegates could face an unpalatable choice: hand the nomination to a candidate who limps to the finish a month from now, or overturn the will of voters and face a backlash among African Americans and of young people energized by Obama's promised break from the past.
The greatest beneficiary, many Democrats fear, will be McCain, the Arizona senator who in effect wrapped up the GOP nomination in February and now runs even with either of the two Democrats in national polls.
"He keeps going into Democratic territory and picking up votes, being a statesman and raising money," said New Mexico Gov. Bill Richardson, a onetime Democratic presidential hopeful who dropped out of the race and has endorsed Obama.
Others warn against premature panic, noting that November races are rarely decided this early. Democrats will rally around their nominee in plenty of time to defeat McCain, they say, even if their preferred candidate loses.
"I think there's going to be a short depression, but I think it's going to be overcome quickly when they recognize what's at stake," said Art Torres, chairman of the California Democratic Party. "That's where we will be unified."
Barabak reported from Bloomington and Decker from Los Angeles. Times staff writers Noam N. Levey in North Carolina and Peter Nicholas in Indiana contributed to this report.