Gun control activist David Hogg apparently thinks President Trump will cancel the 2020 election.

In a tweet Sunday afternoon, Mr. Hogg, who had earlier in the day insinuated that all the National Rifle Association’s 2016 political spending money came from Russia, encouraged people to vote with a stark warning.

“These Midterms could be the last election of our lifetime. VOTE,” he wrote on Twitter.

Mr. Hogg did not elaborate on why he thought that, though a Washington Post poll that came out last week showed that a majority of Republicans answered yes to the question “If Donald Trump were to say that the 2020 presidential election should be postponed until the country can make sure that only eligible American citizens can vote, would you support or oppose postponing the election?”

There is no evidence that Mr. Trump has such a plan or that he would have the power to cancel the election even if he did.

Earlier in the day, Mr. Hogg taunted Sen. Marco Rubio, Florida Republican, by claiming that the NRA is a Kremlin money-laundering front.

In response to a tweet by CNN’s Jake Tapper about Mr. Rubio denouncing the Kremlin on his show, Mr. Hogg replied that “I just find it hilarious that he says he takes money from the NRA because they agree with his agenda.

“My question is does that include @russia giving 30 million to the @NRA to give Trump?” he continued.

There is no publicly available information to that effect.

The figure “$30 million” represents the entire amount the NRA spent to help elect Mr. Trump, according to an article last month in Vanity Fair on ties between several Russians and American gun-rights supporters and NRA officials.

The article offered no proof of Russian donations beyond what the NRA has publicly acknowledged — that since 2015 it has received about $2,500 “from people associated with Russian addresses (which may include US citizens living in Russia), or known Russian nationals living in the United States.” Most of even that small amount was for membership dues and magazine subscriptions, the NRA said.