An Unexpected Struggle for Trump: Defining an Elusive Biden

“It is going to be more difficult for the Trump campaign to go after a man who really is a centrist, has dealings with people across the aisle and knows how to talk to people who disagree with him,” said Priscilla Southwell, a professor emerita of political science at the University of Oregon. “And 2020 is a different kind of year. Donald Trump can appeal to his core by being negative, but it’s such a difficult time for everybody. I don’t think negativity is going to sell as well as it used to.”

Defining an opponent — putting them on the defensive with caricature — is a crucial and proven tactic for candidates in competitive races. There is a graveyard of failed contenders — names like Kennedy, McGovern, Romney, Gore and Hillary Clinton — who found themselves branded by an opponent in portrayals, often unfair, that ricocheted across the political playing field and the media.

Mr. Trump had been adept at this. But the kind of attacks that seemed so effective when he was a new-to-politics outsider in 2016 also appear to have less resonance coming from inside the White House. Four years of tweets by Mr. Trump have numbed many voters.

“It’s almost self-defeating,” said Ron Christie, a Republican who was a senior adviser to President George W. Bush and Vice President Dick Cheney. “People are exhausted. The president, with every tweet, every insult, will move himself out of favor with the demographic that he needs the most, which is the independent.”

Mr. Trump does have some avenues to use against Mr. Biden before voter attitudes begin to harden. He has sought to tie Mr. Biden to the political unrest that has swept the country since the death of George Floyd in Minneapolis on May 25 while in police custody. And Mr. Trump has tried to portray his opponent as senile, “sleepy,” corrupt and an ally of China, but none of those lines of attack has resonated with the public, at least up to now.