MANCHESTER, N.H. - Just under a month before a Feb. 5 mega-primary potentially involving half the voters in the United States, both parties are now without a clear front-runner, with two Democrats fighting for the lead and at least four Republicans jostling to establish themselves as national contenders.
After last night's victories by Hillary Clinton and John McCain, each party now faces the unprecedented intensity of a monthlong scramble with contests in more than two dozen states - including some of the country's most heavily populated - that is certain to strain even the most well-funded campaigns.
"No one has enough money in a primary to run everyplace," said Neil Oxman, a Democratic media consultant.
As a result, candidates will be forced to move limited resources around an electoral map with the goal of simultaneously demonstrating viability to the media and voters, earning credibility with donors and party elites, and accumulating delegates whose count ultimately will determine the parties' nominees.
Each campaign - weighing the relative assets of cash and candidate time - will approach those strategic decisions differently, leaving it unlikely that there will be many state contests where all candidates face one another at full power.
Instead, campaigns will pick places in which they can mount a strong showing or tactically deny one to an opponent.
"Some candidates will go to areas of strength and some will go to areas of rivalry," said Barbara Norrander, a political scientist at the University of Arizona.
Among Republicans, McCain's win following Mike Huckabee's victory in last week's Iowa caucuses sets up the first direct confrontation between the two next Tuesday in Michigan.
McCain won the state in 2000 thanks to overwhelming support from independents, while Huckabee has performed well in recent polls and is counting on the fervor of its evangelical community.
For both candidates, Michigan will provide a chance to dispatch the threat of Mitt Romney, who has slipped to two consecutive second-place finishes and will look at the state, in which he was raised as the son of a popular governor, as his best hope for a comeback.
The following Saturday, McCain and Huckabee will vie for the attention of South Carolina Republicans - this time with added competition from Fred Thompson. The former Tennessee senator came in a distant third in Iowa and abandoned New Hampshire early, choosing to watch the state's primary returns in South Carolina.
"The next couple of weeks will be sorting out who will be the national leader," Norrander said of the Republicans. "If someone wins in a second contest, that will give them a big boost."
Yet former New York City mayor Rudy Giuliani remains committed to looking past both Michigan and South Carolina to focus time and money on Florida, which will vote Jan. 29.
Giuliani's aides reiterated this week that they are willing to concede the first five states - in which Giuliani may finish no better than fourth -- as part of a strategy focused on winning Florida and gaining stature before large coastal states vote the next week.
After her surprise win against Barack Obama in New Hampshire, Hillary Clinton will have to compete under less favorable conditions in Nevada and South Carolina, where Obama has highly energized supporters.
Regardless of the outcomes of those contests, both candidates are likely to marshal resources for Feb. 5, when voters in 22 states - including California, New York, and New Jersey - will go to the polls, amounting to nearly two-thirds of the party's total delegates.
"You ask, 'Where is it most fruitful to go delegate-hunting?' " said Oxman. "You go for delegates-for-dollar. It's not difficult arithmetic."
Yet the calculations candidates make may have to take into account the vagaries of media coverage. In recent primary contests, the news media has followed candidates' standings based on the number of contests won and not delegates collected.
"Voters don't understand the delegate deal at all," said Tom Lindenfeld, a Democratic field strategist. "They really care about states."
The costs of advertising in the states that vote Feb. 5 - which include the nation's most expensive media markets in New York, Los Angeles, and Chicago - is unusually prohibitive. Candidates will be able to afford television ads in only a fraction of them.
"You're better off buying a national spot if you want to advertise in 20 states," said Oxman.
As a result, campaigns will have to rely on their abilities to generate media coverage and volunteers to reach voters.
Even as the campaign expands nationwide, local circumstances will continue to command candidates' attention. Voters in Iowa and New Hampshire overwhelmingly shared similar concerns in each party's primary - immigration and terrorism among Republicans, the Iraq war and healthcare among Democrats - with only small variations.
But as the calendar turns, so will the issues, requiring candidates to adjust deftly.
"In South Carolina, we will be working very hard to engage our natural constituency -- and that is veterans, military," said McCain, who has emphasized his national security credentials and support for the Iraq war while campaigning in the state.
"In Michigan, the issues will be economic," he said in an interview yesterday, noting the state's high unemployment rate and population loss.
"A laid-off worker in Detroit loves the Marine Corps, but his major issue is not the all-volunteer force and the size of the military."