WASHINGTON (AP) -- Republican Donald Trump and Democrat Hillary Clinton are eyeing an opportunity to pull away from their rivals on Super Tuesday, a delegate-rich dash across the country that could accelerate their march toward the general election.
Voters from Vermont to Colorado, Alaska to American Samoa and a host of states in between were heading to polling places and caucus sites on the busiest day of the 2016 primaries.
The contests come at a turbulent moment for Republicans as they grapple with the prospect of Trump becoming the party's nominee. Rivals Marco Rubio and Ted Cruz are engaged in a frantic effort to stop the billionaire -- with Rubio in particular lobbing surprisingly personal attacks -- but it was unclear whether they'd made their move too late.
Trump said his support crossed party lines and has even brought Democrats into the GOP.
"We're getting people into the party that they've never had before," he told ABC's "Good Morning America" on Tuesday. "I can tell you the one person Hillary Clinton doesn't want to run against is me."
Like Trump, Clinton has won three of the four early voting contests, including a thrashing of rival Bernie Sanders in South Carolina on Saturday. Her victory there was due to overwhelming support from black voters, putting her in position for a strong showing in several Southern states with large African-American electorates that vote Tuesday.
Clinton has increasingly turned her attention to Trump in recent days, casting herself as a civil alternative to the insults and bullying that have consumed the Republican race.
"What we can't let happen is the scapegoating, the flaming, the finger pointing that is going on the Republican side," she told voters gathered in Springfield, Massachusetts. "It really undermines our fabric as a nation. So, I want to do everything I can in this campaign to set us on a different course."
Sanders, who has energized young voters with his call for a political revolution, was seeking to stay close to Clinton in the South and pick up victories in states including Minnesota and his home state of Vermont. But Sanders faces tough questions about whether he can rally minorities that are core Democratic voters.
After he voted Tuesday in his hometown of Burlington, Vermont, Sanders told reporters that if voter turnout is high "we are going to do well. If not, we're probably going to be struggling."
Democrats will vote in 11 states and American Samoa on Tuesday, with 865 delegates up for grabs. Republicans will vote in 11 states, with 595 delegates at stake.
Trump was seeking to sweep the South, which would be a massive blow for Cruz. The Texas senator, a favorite of the region's social conservatives and evangelical Christians, expected the South to be his firewall, but now is simply hoping to emerge with a victory in his home state.
Rubio's goal on Super Tuesday is even more modest. He's seeking to stay competitive in the delegate count and hopes to pull off a win in his home state of Florida on March 15.
The Florida senator has cast himself as Republicans' best chance to win in a general election and has received a flood of endorsements from GOP officials after other more mainstream candidates dropped out. But he's failed to win a state so far, raising questions about his strategy for topping Trump.
Republicans spent months largely letting Trump go unchallenged, wrongly assuming that his populist appeal with voters would fizzle. Now party leaders are divided between those who pledge to fall in line behind Trump if he wins their party's nomination and others who insist they can never back him.
An Associated Press survey of GOP senators and governors across the country showed just under half of respondents would not commit to backing Trump if he's the nominee. Their reluctance foreshadowed a potentially extraordinary split in the party this fall.
"If he becomes the nominee the Democrats are going to savage him, no question about it," GOP Utah Sen. Orrin Hatch said. His Republican colleague from Arizona, Jeff Flake, said he was "still holding out hope" that he wouldn't have to make the choice about supporting Trump.
The worries among Republicans appeared to grow after Trump briefly refused to disavow former Ku Klux Klan leader David Duke during a television interview. Trump said he had not understood the interviewer who first raised the question about Duke, and he did later repudiate him.
House Speaker Paul Ryan, who said Tuesday he is trying to stay out of the "day-to-day ups and downs of the primary," nonetheless took time on the busiest voting day of the year to date to say anyone who wants to be the Republican presidential nominee must reject any racist group or individual.
"When I see something that runs counter to who we are as a party and a country I will speak up. So today I want to be very clear about something: If a person wants to be the nominee of the Republican Party, there can be no evasion and no games. They must reject any group or cause that is built on bigotry," Ryan said.
States holding voting contests in both parties Tuesday are Alabama, Arkansas, Georgia, Massachusetts, Minnesota, Oklahoma, Tennessee, Texas, Vermont and Virginia. Republicans vote in Alaska and Democrats in Colorado. Democrats also have a contest in American Samoa and for Democrats Abroad.
Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.