But instead of joining the offensive, Mr. Kaine has been deployed as humanizer in chief, aiming to shore up Mrs. Clinton’s low marks for trustworthiness, and to answer questions she could answer herself, except that she hasn’t held an open news conference since December. Last week, Mrs. Clinton and her surrogates doubled down on her claim that James Comey, the F.B.I. director, said her public statements about her emails were truthful. He did not, and they were not.

On Sunday, Mr. Kaine was asked on NBC News’s “Meet the Press” to explain Mrs. Clinton’s serial misstatements about her emails. He struggled, saying he had heard Mrs. Clinton say, “I made a mistake and I’ve learned something,” adding, “I’ve heard her apologize.” If Mrs. Clinton becomes president, Mr. Kaine said, “We’re going to be real transparent, absolutely.”

A far more onerous rescue effort is taking place on the Trump side, where Mr. Pence has spent three weeks struggling to convince his own party that Mr. Trump is not only trainable, but sane. As Mr. Trump’s insults and incoherent statements pile up, Republicans have begun calling for Mr. Pence to leave the ticket, or pressure Mr. Trump to quit.

On Monday, as Mr. Pence was headed to Detroit for Mr. Trump’s big economic speech, the conservative radio commentator Charlie Sykes — whom Mr. Trump has called a “dope” — asked the vice-presidential nominee, “Can you or anyone else get Mr. Trump to stop saying crazy and offensive things for the next three months?”

Mr. Pence replied: “Ha ha, well, um yeah, you always hear these rumors. It just, you know, I guess it makes for good fodder on the internet. On a regular basis going forward, you’re going to see Donald Trump laying out specific policy proposals for how we rebuild this country at home and abroad.” That was Monday, before Mr. Trump invited gun owners to devise some way of stopping Mrs. Clinton’s agenda.