Polls suggest that voter disapproval has hardened during his time in office, even if most of his base remains firmly behind him. For a president whose approval rating has consistently placed in the 40s, and who won the White House by capturing Pennsylvania, Michigan, and Wisconsin by less than 1 percentage point each, there is little margin for error.
"Donald Trump drew an inside straight in 2016. The question remains whether he can draw an inside straight two hands in a row," said Whit Ayres, a Republican pollster who advised U.S. Sen. Marco Rubio, R-Fla., during his presidential campaign. "The president has done virtually nothing to expand the coalition of the people who support him, in lieu of energizing and reinforcing the people who are already with him."
Unlike in 2016, when Trump won over many voters by making Hillary Clinton an unacceptable alternative, this race will be a clear referendum on the incumbent, said Lara Brown, an associate professor at George Washington University's School of Political Management. She pointed to polling that suggests some of the soft supporters who gave Trump a chance because they didn't like Clinton or wanted a change have turned against him.
"President Trump is in a very precarious position," Brown said. "If we look at where the independents are today vs. where they were on Election Day (2016), he has lost ground."
In Minnesota, Michigan, Pennsylvania, Ohio, and Wisconsin -- key Rust Belt states that could swing the election -- Trump's average disapproval rating has grown by around 13% since his inauguration, she said, citing data from Morning Consult, a polling company that conducts regular surveys.
"Trump has only hardened perceptions of his character and behavior over time," Brown said.
His campaign launch could do the same. Four years after riding down an escalator in Trump Tower and describing Mexican immigrants as drug dealers and rapists, Trump preceded his reelection rally by announcing plans for deporting "millions of illegal aliens," starting next week.
He did it, of course, on Twitter.
"He's got some very real problems, and I suspect his announcement will exacerbate his problems, because his announcement will be pitched to the base," said Robert Shrum, a longtime Democratic consultant who is now a professor at the University of Southern California. "He's doubling down on the strategy that has gotten to somewhere between 38 and 42% approval."
Indeed, Trump spent most of his more than hourlong speech reprising familiar grievances against Democrats, the news media, the special counsel investigation into Russian interference, and Clinton.