Donald Trump is a candidate without a campaign - and it's becoming a serious problem.

Republicans working to elect Trump describe a bare-bones effort debilitated by infighting, a lack of staff to carry out basic functions, minimal coordination with allies and a message that's prisoner to Trump's momentary whims.

"Bottom line, you can hire all the top people in the world, but to what end? Trump does what he wants," a source close to the campaign said.