Voters weary of the taunts and insults of the 2016 primary season may pine for a White House campaign about issues. But the Hillary Clinton versus Donald J. Trump showdown is almost sure to disappoint them. It has quickly deteriorated into a scorched-earth contest about personality and temperament, with each side exploiting voters’ strong dislike of the other candidate.

“We have an explosive environment with two extremely negative candidates,” said Ed Goeas, a Republican pollster. “This is going to be a race to the bottom. It’s who can drive up the negatives the most.”

Mr. Trump accused Mrs. Clinton over the weekend of abetting her husband’s infidelities by seeking to tarnish his accusers. He labeled her a “nasty, mean enabler.”

Allies of the Clinton campaign taunted Mr. Trump as “Dangerous Donald,” meant to raise fears of him gaining control of America’s nuclear arsenal, a charge soon to be echoed by more than $100 million in negative ads from a “super PAC” that successfully tarnished the 2012 Republican nominee, Mitt Romney.