U.S. President Joe Biden ripped several of his possible Republican 2024 election opponents on Monday, including saying that his predecessor Donald Trump lacked the "courage" to stop the Jan. 6, 2021, attack on the Capitol.

"The police were heroes that day: Donald Trump lacked the courage to act," Biden said in taped remarks to the National Organization of Black Law Enforcement Executives Conference.

"The brave women and men in blue all across the nation should never forget that. You can't be pro-insurrection and pro-cop. You can't be pro-insurrection and pro-democracy. You can't be pro-insurrection and pro-American."

His remarks for the Florida event included jabs at other prominent Republicans in the state such as Governor Ron DeSantis, a rising star in the party regarded as a possible presidential contender.

"In the state you're in today, Governor DeSantis, Senator Marco Rubio, Senator Rick Scott all opposed banning assault weapons," said Biden, who has been recuperating from COVID in isolation at the White House.

"To me it's simple: You can't support bringing weapons of war on American streets; you're not on the side of police."

Biden generally refrains from discussing his political foes by name. Trump and DeSantis have both flirted with the possibility of challenging Biden in the 2024 elections.

Midterm elections on Nov. 8 will determine whether Biden's Democratic Party retains control of Congress and are regarded as a test of the arguments that will be made to voters for and against a second, four-year term for Biden.

Biden's comments united several hot-button themes - law enforcement, guns and threats to democracy - on which Democrats hope to put Republicans on the defensive.

Trump branded himself an ally of gun owners, the police and "law and order" after protests over racial brutality. Biden, who last month signed a bipartisan gun safety bill into law, has sought to make the case that further measures like those will keep police safe.

In the Capitol attack, thousands of Trump supporters breached the building in an attempt to stop Congress from certifying Biden's November 2020 presidential election victory.

Over the past six weeks, a U.S. House of Representatives panel has laid out a case that the president stoked the violent mob and then sat back and watched.

Trump and many Republican lawmakers have dismissed the Jan. 6 committee as politically motivated even though it relies on testimony from the Republican former president's aides and allies.

Biden allies think the hearings could cause Trump supporters to re-think their allegiance. A Reuters/Ipsos poll last week found that 32% of Republicans say Trump should not run for president in 2024, up from 26% who said that at the start of the hearings.