Sen. Bernie Sanders (I-Vt.) and former vice president Joe Biden hit the campaign trail Monday on the eve of another day of key contests in the Democratic presidential primary, amid mounting concerns about the spread of the novel coronavirus.

Six states will vote on Tuesday: Idaho, Mississippi, Michigan, Missouri, North Dakota and Washington. Biden picked up key endorsements in recent days as two of his formal rivals — Sens. Kamala D. Harris (D-Calif.) and Cory Booker (D-N.J.), threw their support behind his campaign.

Both Sanders and Biden have said they are heeding the advice of public health officials as the number of confirmed U.S. coronavirus cases surpassed 500 on Sunday. Rep. Tulsi Gabbard (D-Hawaii) is also competing for the Democratic presidential nomination.

President Trump, meanwhile, is holding a fundraiser in Florida, in a departure from his typical practice of holding a “Keep America Great” rally on the eve of a Democratic primary or caucus.