Jared Kushner, President Donald Trump's son-in-law and White House adviser, has reportedly advised the president to lay off the 2020 Democratic candidates, at least for the time being.

"Basically what he has advised the campaign is, now is not the moment for them to be making news or attacking anyone," one person with knowledge of Kushner's strategy told Politico.

But the president hasn't been able to stop himself from repeatedly attacking one candidate in particular: former Vice President Joe Biden.

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Jared Kushner, President Donald Trump's son-in-law and White House adviser, has reportedly advised him to lay off the 2020 Democratic presidential candidates, at least for the time being, Politico reported Thursday.

"Basically what he has advised the campaign is, now is not the moment for them to be making news or attacking anyone," one person with knowledge of Kushner's strategy told Politico.

But the president hasn't been able to stop himself from repeatedly attacking one candidate in particular: former Vice President Joe Biden.

Trump raged at Biden on Twitter on Wednesday after the International Association of Firefighters, a key labor union, endorsed the former vice president.

"I've done more for Firefighters than this dues sucking union will ever do, and I get paid ZERO!" Trump wrote, and re-tweeted about 60 Twitter accounts who claimed to be firefighters who support his presidency.

Some of the president's advisers and campaign aides are concerned that Biden is the strongest Democratic contender, and that the president's attention will grow Biden's influence.

"We've asked him — I've personally asked him — to stop. It's not helping us. It's helping Biden," a Trump adviser told Politico. "We don't think Biden can make it out of the woke Democrat primary. But he will if the president gives him oxygen."

Read more: Here's where 2020 Democratic presidential candidates stand on impeaching Trump

Biden appears pleased to be viewed as a threat by the president.

"I understand the President has been tweeting a lot about me this morning," he said during a Wednesday rally in Iowa. "I wonder why the hell he's doing that."

Meanwhile, Biden has made attacking Trump a cornerstone of his campaign thus far, unlike many other 2020 candidates. He announced his candidacy with a campaign video heavily focused on Trump's controversial response to the deadly 2017 white nationalist rally in Charlottesville, Virginia.

And Trump has responded by repeatedly attacking Biden beginning even before the former vice president entered the race late last month.

"Welcome to the race Sleepy Joe. I only hope you have the intelligence, long in doubt, to wage a successful primary campaign," Trump tweeted shortly after Biden's announcement. "It will be nasty — you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate!"