WASHINGTON — 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.

“This is a movement,” Trump told supporters at a rally Monday evening in Georgia. “I’m just a messenger, folks.”

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.

Democrats will vote in 11 states and American Samoa today, 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.