President Biden remains the front-runner for the Democrats and doesn't face any serious challengers. Among the states voting on Tuesday is Minnesota, the home state of Rep. Dean Phillips, who has launched a longshot bid against Mr. Biden and could face defeat in his home state. Although author Marianne Williamson had ended her long-shot campaign, she unsuspended it after she finished ahead of Phillips in the Michigan primary.

Former President Donald Trump is the front-runner for the Republican nomination, but former United Nations Ambassador Nikki Haley is still in the race. Haley has yet to win any states, although she has picked up some delegates along the way. 

There are hundreds of delegates at stake for both Democrats and Republicans on Super Tuesday, but neither Mr. Biden nor Trump will be able to win enough delegates to secure the nomination on March 5. CBS News estimates that the earliest Mr. Trump can clinch the nomination is March 12 and the earliest Mr. Biden can is March 19.