The U.S. presidential candidates are using Monday to make a last push for support before voters in 11 states have their say in who should be the nominees for the Democratic and Republican parties.
Republicans are focusing on the South, which accounts for two-thirds of the delegates that will be awarded on what is called Super Tuesday.
Businessman Donald Trump, the front-runner in the Republican race, is holding events in Virginia and Georgia, while Florida Senator Marco Rubio is campaigning in Arkansas.
Texas Senator Ted Cruz is focusing his efforts on his home state, which offers 155 of the roughly 600 delegates at stake for Republicans Tuesday.
Trump and Rubio continued their attacks against each other on Sunday.
WATCH: Republican candidates Trump, Cruz in Texas showdown
Rubio called the billionaire a "con artist" and joked about his tan complexion, saying Trump will "make America orange." He also told supporters Republicans cannot nominate someone "who refuses to condemn white supremacists."
Trump declined in a television interview early Sunday to denounce an endorsement by white supremacist David Duke, but later said on Twitter he disavows it.
He also responded to criticisms about retweeting a quote from World War Two-era Italian dictator Benito Mussolini, saying he thought it was a "very interesting" remark.
Trump used the online platform to attack Rubio's work in the Senate, and repeatedly derided him as "Little Marco Rubio."
Meanwhile, Cruz asserted that Trump would likely lose in a general election match-up with Democrat Hillary Clinton, and said Trump "doesn't even know what he'd do" as president should he win the race to the White House.
But Cruz acknowledged in an interview with CBS' Face the Nation that "there is no doubt that if Donald steamrolls through Super Tuesday, wins everywhere with big margins, that he may well be unstoppable" to win the Republican nomination.
Trump has already won three of the first four states to hold Republican nominating contests.
Clinton, the former secretary of state, has a chance to significantly add to her already big lead over Vermont Senator Bernie Sanders in the Democratic race.
Both will hold events Monday in the northeastern state of Massachusetts, with Clinton then going to Virginia and Sanders traveling to the northern state of Minnesota.
Clinton is favored in most of the states voting Tuesday, but the Sanders campaign said it has a good shot at winning five of the states, especially ones outside of the southern states where black voters favoring Clinton comprise a large part of the Democratic electorate.
Sanders is expected to win in his home state of Vermont, where few delegates are at stake, and also contend in neighboring Massachusetts, the western state of Colorado and Minnesota.
WATCH: In Democratic races, Clinton is favored Tuesday, but Sanders to attract youth vote