Indiana Gov. Mike Pence speaks during the Indiana Republican Party Spring Dinner last week in Indianapolis. Darron Cummings/AP hide caption

Presidential candidate Donald Trump participates in a town hall meeting for MSNBC with Chris Matthews. Tom Lynn/Getty Images hide caption

A U.S. Border Patrol agent looks out over Tijuana, Mexico, next to a portion of the U.S.-Mexico border wall. Gregory Bull/AP hide caption

Corey Lewandowski, campaign manager for Republican presidential candidate Donald Trump, at a campaign rally in Palm Beach, Fla. earlier this month. Joe Raedle/Getty Images hide caption

Wisconsin Gov. Scott Walker announces he is suspending his presidential campaign at a news conference in Madison in September. Morry Gash/AP hide caption

Republican presidential candidate Donald Trump makes a boxing gesture while greeting the crowd after speaking at a campaign rally in New Orleans earlier this month. Trump won Louisiana, but Ted Cruz is likely to end up with more delegates from the state. Gerald Herbert/AP hide caption

Donald Trump speaks during a campaign event in the atrium of the Old Post Office Pavilion in Washington, D.C. It is soon to be a Trump hotel. Alex Brandon/AP hide caption