His ominous remarks were a concession to his political standing: trailing in the polls, lacking a booming economy or a positive message to campaign on, and leaning on culture wars to buoy his loyalists.

In a speech at the White House on Saturday evening and an address in front of Mount Rushmore on Friday night, Mr.

He signaled even more clearly that he would exploit race and cultural flash points to stoke fear among his base of white supporters in an effort to win re-election.

Trump followed up with his remarks on Saturday from the South Lawn of the White House, which sounded more like a campaign rally, and repeated the themes from the previous evening.

Few on the White House South Lawn were wearing masks.

The president repeated his false claim that an abundance of testing made the country’s cases look worse than they were because they “show cases, 99 percent of which are totally harmless.” And he raised expectations for a vaccine “long before the end of the year.”.

His remarks at Rushmore, and repeated from the grounds of the White House, were a reflection of his dire political standing as he nears the end of his first term in office.

Trump is trailing former Vice President Joseph R.

Biden Jr., the presumptive Democratic nominee, in national and battleground polls; lacks a booming economy or a positive message to campaign on as he tries to assign blame elsewhere for the spread of the coronavirus; and is leaning on culture wars instead to buoy his base of white supporters.

Campaign officials said Saturday that they thought the speeches struck the right note for the moment.

Campaign officials have repeatedly said they expect backlash against the progressive “cancel culture” movement to help the president’s standing with white suburban female voters, who they believe to be frightened by images of chaos in the city streets.

“Donald Trump does not give you that choice — you are either with him or against him,” said Mr.

Biden, for instance, has said he does not support defunding the police, and has made careful distinctions between tearing down monuments to the country’s founding fathers and those commemorating Confederate leaders.

Trump had never weighed in on the immigration debate before he made building a wall along the Mexican border the signature issue of his 2016 presidential campaign because he saw that it worked