The 71-year-old McCain's political rebirth also gave his once-struggling campaign new life and put him in the midst of a wild scramble for the Republican nomination that has produced no clear favourite.
"This state can again play a key role. We won here in 2000 and we will win again in 2008," McCain, whose presidential bid collapsed in 2000 shortly after his Michigan win, told an airport rally in Grand Rapids.
Michigan shaped up as a must-win for Romney, 60, the former Massachusetts governor, who spent heavily in Iowa and New Hampshire but finished second in both states. Romney's campaign suspended advertising in South Carolina and Florida to concentrate on Michigan.
"We feel the best strategy for us is to direct all our efforts toward Michigan. That's where the next playing field is," said Romney spokesman Kevin Madden.
New Hampshire's voters refused to follow the lead of Iowa, which last week gave Democrat Obama, 46, and Republican former Arkansas Gov. Mike Huckabee, 52, the first big wins of the U.S. presidential race.
Huckabee, a Baptist minister who has risen partly on the support of evangelicals, flew to South Carolina before the state's Republican showdown on January 19. He said his Southern roots would help there.
"Certainly there's a deep connection I have with people in the South, there's a greater familiarity," Huckabee told reporters aboard his plane.
'MOMENT OF CONNECTION'
The typically stoic Clinton conceded an emotional moment during a pre-election rally on Monday, in which she came close to tears as she discussed her reasons for wanting the presidency, may have helped her.
"I had this incredible moment of connection with the voters of New Hampshire and they saw it and they heard it," she said on CBS' "Early Show."
Clinton, 60, who finished third in Iowa, faced predictions of doom before New Hampshire. Polls showed her trailing Obama by double-digits, but she pulled out a narrow win.
Obama had hoped a New Hampshire win would solidify his hold on the top spot in the race.
Instead, his campaign turned to Nevada and in particular South Carolina, where more than half the Democratic primary voters are expected to be black.
Both Obama and Clinton reported big fundraising numbers in the last three months of 2007, with Clinton bringing in $24 million for the nominating race and Obama $22.4 million. Obama raised $8 million in the first eight days of 2008.
