Donald Trump's behavior in recent days, from criticizing the parents of a fallen American soldier to declining to endorse House Speaker Paul Ryan, has strained the nerves of his campaign staff as he falls behind in the polls.

I exchanged messages Tuesday evening with a longtime ally of Trump campaign manager Paul Manafort, whom I asked about who was calling the shots in the campaign. The response indicated that Manafort, a veteran of Republican politics brought in this spring for the transition from primaries to the general election, has lost control over his candidate.

"Manafort not challenging (Trump) anymore," Manafort's ally wrote. "Mailing it in. Staff suicidal."

After I tweeted those remarks, Trump campaign spokesman Jason Miller wrote to me, "The idea that Paul Manafort's mailing it in is completely erroneous. Our campaign just finished up our strongest month of fundraising to date, we're adding talented and experienced staffers on a daily basis, and Mr. Trump's turning out bigger, more enthusiastic crowds than Hillary Clinton ever could."