As the race for the Democratic nomination revs up, the opposition research is proliferating. And Fox News hosts have begun amplifying rumors about Joe Biden's health, echoing similar attacks on Hillary Clinton during the 2016 campaign.

The Daily Beast reports that on at least four occasions, Fox News has brought up Biden's health.

“He is much more like Hillary Clinton, because if you talk to Democrats, who are working for different campaigns, all of the aggressive gossip whisperers—and this is where the action is happening in terms of opposition research—it’s people having a few drinks at a bar and whispering, ‘You know there is something wrong with the former vice president,’” Fox host Lisa “Kennedy” Montgomery claimed. “But that’s what they are actively doing right now. And it is surprising because they are concerned with taking Biden down and getting their candidate out there.”

“I was thinking more along the lines of Hillary Clinton having a lumpy overcoat in 85-degree weather,” she added, a reference to rumors that emerged after Clinton was photographed in a heavy coat.

The Mueller probe revealed that Republican operative Roger Stone had played a key role in spreading unfounded rumors about Clinton's health.

Biden, at 77, is the second-to-oldest candidate in the race.