In an interview Thursday President Trump praised 2020 presidential hopeful Bernie Sanders as "smarter" than his rival, Joe Biden.

According to reports, Trump has privately expressed respect for Sanders' political acumen, and ability to draw large crowds.

But the president's praise could be a tactic to sow division in the Democratic Party. According to advisers, Trump is looking for opportunities to "cause chaos from the left and right."

Sanders is popular with the white working class voters in swing states who were key to Trump's victory in 2016.

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To his millions of Twitter followers President Trump denounces 2020 presidential candidate Senator Bernie Sanders of Vermont as "crazy," and even launched into a mocking impersonation of Sanders' mannerisms at a raucous rally in August.

But in remarks to Boston Herald radio on Thursday, the president indicated that he may have more respect for the veteran left-wing senator than he usually lets on.

Discussing his rivals for the presidency in 2020, the president remarked of Democratic front-runner Joe Biden "In many ways, I like him" — but added "he's not as smart as Bernie [Sanders]. And he's not as quick." The president has previously named the two as the Democrats most likely to challenge him for the presidency in 2020.

Sources close to the president told the Daily Beast in April that though he believes he would beat Sanders in next year's election, he has expressed grudging respect for Sanders' political acumen, ability to draw large crowds, and his campaign's fundraising haul from small-scale donors.

So why does the president think Sanders — whose chances in 2020 many top Democrats and pundits have written off — is a serious challenger?

The answer lies in Sanders' appeal to white working class voters in Rust Belt states, thousands of whom swung to the Republicans in 2016, delivering Trump the presidency.

Sanders launched his presidential bid with a tour of Wisconsin, Indiana, Michigan, Ohio and Michigan, pitching his populist message, and telling voters that Trump betrayed them when he pledged in 2016 to renew the American working class.

He has even made a direct pitch to Trump's voters on the president's favorite news channel, Fox News, leading the president to angrily denounce the network for hosting his rival.

There is, of course, another possibility: that Trump is praising Sanders to sew division in Democrat ranks, masking his real fear that Biden is best placed to beat him in 2020.

Former vice president Biden also commands strong support in some of the swing states that voted for Trump in 2016.

Joe Biden, the current favorite to secure the Democratic presidential nomination. AP Photo/Keith Srakocic

An adviser to the president told CNN in February that Trump is tuning in closely to the Democratic primaries, looking for opportunities to "cause chaos from the left and right."

In 2016 Trump pitched to Sanders supporters by pledging to renew American manufacturing and accused the Clinton campaign and Democratic establishment of stitching up the party nomination to deny him victory. In the end, more than 10% of Sanders supporters ended up voting for Trump in 2016 over Clinton.

Advisers to the president told the Daily Beast that though Trump harbors respect for Sanders, he relishes the propect of facing him in 2020 should Sanders upset the odds and win the Democratic nomination, and would paint him as a dangerous radical who would throw America into same the economic chaos faced by countries like Venezuela.

Though Trump's adviser and son-in-law Jared Kushner has reportedly urged the president to stay out of the Democratic primaries, Trump seems intent on stirring conflict between Democratic centrists who back Biden, and left-wing populist who support Sanders.