US President Donald Trump previously decried former Vice President Joe Biden as a "dummy" and said former President Barack Obama "pulled him out of the trash heap," but Politico reports that Trump is concerned about a possible Biden candidacy.

Trump's allies are also reportedly concerned that Biden could give Trump fierce competition in Rust Belt states that Trump carried in 2016, including Pennsylvania, Michigan, Wisconsin, and Ohio.

But aides to the president reassure him that Biden is too centrist and friendly to Republicans to win the Democratic base in a primary.

President Donald Trump's aides are reassuring Trump that despite former Vice President Joe Biden's strong performance in early Democratic polls, he won't be progressive enough to win the nomination, according to a report from Politico.

Biden, who served as President Barack Obama's vice president and a US Senator for 36 years, has hinted at a presidential run for months.

While Trump has previously decried Biden as a "dummy" and said Obama "pulled him out of the trash heap," Politico reports that he frequently asks aides for updates on Biden's poll numbers.

Trump's allies are also concerned that Biden, who hails from Scranton, Pennsylvania, could give Trump fierce competition in Rust Belt states that Trump carried in 2016, including Pennsylvania, Michigan, Wisconsin, and Ohio, sources told Politico.

While most early primary polls have Biden in first place, polls conducted almost 11 months before the first primary contest aren't necessarily indicative of who will succeed at the ballot box.

Even though Biden has high name recognition and is widely beloved within the Democratic Party, he ideologically fits in the center of the party at a time when many candidates are leaning toward more progressive policies.

One friend of Trump told the president that he shouldn't worry about Biden being the nominee because "the Democratic base is looking for someone newer, fresher," Politico said.

Read more: Biden's long history in public life could come back to haunt him if he decides to run for president

Biden will have to contend with some of the controversies from his almost five decades in public service. Allies have also told Trump that Biden's previous support for the controversial 1994 crime bill that is widely credited for contributing to mass incarceration will undermine his candidacy with voters concerned about criminal justice.

Some of Biden's remarks from the 1970s in which he argued against the government playing a role in racially integrating public schools with busing have also resurfaced. And, more recently, Biden has caught heat from fellow Democrats for praising Republicans, including Vice President Mike Pence.

Biden apologized for calling Pence "a decent guy" after facing a slew of backlash from fellow Democrats over Pence's anti-LGBTQ record and has been criticized for appearing at events for a Republican congressional candidate in Michigan last fall.

One person close to Trump said Biden's walking back his praise of Pence was "indicative of the fact that this guy is going to be so beholden to the left, if he can’t even make a simple statement about his successor without kowtowing a minute later," according to Politico.