Exclusive: Donald Trump 'Disappointed' in Ohio Gov. John Kasich for Not Endorsing

Trump sat down with ABC News' David Muir for an interview Monday in Ohio.

Like Kasich, Trump signed the RNC pledge assuring that he would support the Republican nominee and not make a third-party bid for the presidency. But after Kasich dropped out of the race for the White House and it became clear that Trump would win the nomination, Kasich would not throw his support behind Trump.

Pence said they were in contact with Kasich.

“I hold Gov. Kasich in high regard. Look, these two went through a tough competition together,” Pence said of Trump and Kasich. “I respect that, these things sometimes take time.”

Ohio is a battleground state and a key state for Trump to win. Polling in the Buckeye State shows a tight race between Trump and Clinton. Ohio has voted for the winner of every election since 1960.