By John Whitesides, Political Correspondent
McCain's coast-to-coast "Super Tuesday" wins in crucial states put him on the verge of a stunning political comeback, but the Democratic picture grew murkier after mixed results on the biggest day of voting to choose candidates for November's presidential election.
"We will unite the party behind our conservative principles and move forward to the general election in November," McCain told reporters in Phoenix.
Republican rivals Mitt Romney and Mike Huckabee vowed to fight on but could face growing questions about their viability. Romney won seven states and Huckabee five on Tuesday.
Both camps said they performed better than expected on Tuesday and tried to lower expectations for the upcoming round of seven Democratic contests in the next six days.
'SCRAPPY LITTLE TEAM'
The Democrats will square off in Louisiana, Nebraska and Washington on Saturday, Maine on Sunday, and Virginia, Maryland and the District of Columbia on Tuesday.
Both the Obama and Clinton camps said the likelihood of a race lasting into the summer was growing.
Obama, an Illinois senator who would be the first black U.S. president, and Clinton, a New York senator who would be the first woman U.S. president, continued their dominance in crucial Democratic voter blocs.
All three of the senators in the presidential race -- Obama, Clinton and McCain -- were returning to Washington on Wednesday to vote on an economic stimulus package in the Senate.
Romney, a former Massachusetts governor and wealthy venture capitalist who has spent at least $35 million of his own money on the race, has argued McCain lacks the conservative credentials to be the party nominee.
Huckabee said fund-raising has picked up and he expected to be competitive in upcoming contests in Virginia, Kansas and Texas.
(Additional reporting by Steve Holland, Jeff Mason, Andy Sullivan, Donna Smith; Editing by Bill Trott)
