President Trump has been privately attacking the GOP candidate in the Pennsylvania House special election, Axios reported Sunday.

Trump has slammed Republican Rick Saccone as a bad and "weak" candidate, four sources told the news outlet.

He reportedly shared his opinion of the GOP candidate before traveling to Pennsylvania to stump for Saccone on Saturday. Axios reported that it's unclear if Trump's opinion of the candidate has changed since then.

Trump largely spent the rally touting his own achievements instead of discussing the candidate, but did endorse Saccone.

"This guy should win easily, and he's going to win easy. You got to know him. He's an extraordinary person. Go out and vote on Tuesday for Rick Saccone," Trump said of the current GOP state lawmaker.

"This administration has already made unprecedented progress on behalf of the American people and I look forward to working with him to continue to deliver on the promises made," Saccone said in a statement following Trump's appearance. "I could not have asked for a stronger endorsement of our campaign ahead of the March 13 special election."

The special election has emerged as a surprisingly competitive race after Trump won the district by nearly 20 points in 2016.

A poll released Friday found that Democrat Conor Lamb holds a 4-point lead over Saccone, and RealClearPolitics has labeled the race a "toss-up."