Photos: On the campaign trail

Ohio Gov. John Kasich speaks during a campaign stop at the MAPS Air Museum in North Canton, Ohio.

Democratic presidential candidate Hillary Clinton arrives at a campaign event with the Chicago Journeymen Local Plumbers Union.

Florida Sen. Marco Rubio has declined to withdraw his criticism of Donald Trump as the GOP nominee.   (Paul Sancya / Associated Press )

U.S. presidential hopeful Donald Trump addresses a rally in Vienna Center, Ohio.

Ohio Gov. John Kasich speaks during a campaign stop at Westerville Central High School in Westerville, Ohio.

Democratic presidential candidate Hillary Clinton and MSNBC’s Chris Matthews during a break in taping a town hall at the Old State Capitol in Springfield, Ill.

Republican presidential candidate Marco Rubio speaks during a campaign rally at Palm Beach Atlantic University in his home state of Florida.

Republican presidential candidate Donald Trump speaks to supporters at Youngstown Airport on in Vienna, Ohio.

Republican presidential candidate John Kasich, left, accompanied by former Republican presidential candidate Mitt Romney arrive for a campaign stop at the MAPS Air Museum in North Canton, Ohio.

Democratic presidential candidate Bernie Sanders greets the crowd at a campaign rally in Charlotte, N.C.

Republican presidential candidate Ted Cruz speaks to guests gathered for a rally at Abbington Banquets in Glen Ellyn, Illinois.