CHARLOTTE, N.C. — President Donald Trump and his fellow Republicans opened their national convention on Monday by painting a dire portrait of America if Democrat Joe Biden wins the White House in November, arguing he will usher in an era of radical socialism.

Mr. Trump set the tone early in the day when he addressed Republican delegates in Charlotte, North Carolina, after formally securing the party’s nomination for another term, and claimed without evidence that Democrats were trying to steal the election.

Republicans had vowed to offer an inspiring, positive message in contrast to what they characterized as a dark and gloomy Democratic convention last week. But the first night’s prime-time program featured speakers who peppered their remarks with ominous predictions if Democrats win power.

“They’ll disarm you, empty the prisons, lock you in your home and invite MS-13 to live next door,” US Representative Matt Gaetz, one of Mr. Trump’s staunchest backers in Congress, said, referring to an international criminal gang.

The four-day convention got under way at a critical juncture for Mr. Trump, who trails Biden in national opinion polls during a pandemic that has killed more than 176,000 Americans, erased millions of jobs and eroded the president’s standing with voters.

Mr. Trump has focused on a “law and order” message in response to widespread protests following the police killing of George Floyd, a Black man in Minneapolis, and he has pushed schools and businesses to reopen despite the pandemic. Both messages represent the campaign’s effort to win back suburban voters, especially women, who have abandoned the Republican Party in droves during the Trump era.

Donald Trump, Jr., the president’s oldest son, portrayed the ongoing civil unrest as violent assaults on small businesses by anarchists and said Democrats would fail to keep neighborhoods safe.

The convention’s opening night also laid out what promises to be a central theme of the week: that Biden, a former vice president, and his running mate, US Senator Kamala Harris, will merely be puppets of radical left-wing activists.

Multiple speakers accused Mr. Biden of wanting to defund the police and ban fracking, though he has rejected both positions.

Another frenetic day for Mr. Trump threatened to overshadow his attempt to recalibrate the campaign, however. In Washington, congressional Democrats examined US Postmaster General Louis DeJoy, a Mr. Trump donor, over whether he was deliberately sabotaging mail service to harm voting by mail, while one of Mr. Trump’s closest advisers, Kellyanne Conway, prepared to depart the White House.

The New York attorney general’s investigation into Trump’s family business deepened on Monday, while the National Guard was deployed in Wisconsin following unrest after a Black man was shot in the back by police.

A Reuters investigation revealed a sex scandal involving evangelical leader Jerry Falwell, Jr., a high-profile Trump supporter, whose tenure at the Christian university he runs appeared in limbo.

In contrast to the Democratic convention, which featured three former presidents, the Republican event does not include former Republican President George W. Bush, who has declined to endorse Trump’s reelection.

Mr. Biden, 77, and his fellow Democrats portrayed Mr. Trump, 74, as a force for darkness, chaos and incompetence during their convention, while stressing the Democrats’ diversity and values like empathy and unity.” — Reuters