President Donald Trump has expressed concern that he could be impeached when Democrats take over the House, a source close to the President told CNN Monday. The source said Trump sees impeachment as a "real possibility.”

But Trump isn't certain it will happen, the source added.

A separate source close to the White House told CNN that aides inside the West Wing believe "the only issue that may stick" in the impeachment process is the campaign finance violations tied to former Trump attorney Michael Cohen's payouts to Trump's alleged mistresses.

Prosecutors endorsed the allegation in a sentencing document for Cohen on Friday, in which they said Cohen should receive a "substantial sentence" for the crimes he committed, which included campaign finance violations for the payments to the two women, tax fraud and lying to Congress. Impeachment talk has ratcheted up in recent days following a blockbuster filing from prosecutors in the Southern District of New York. In that filing, prosecutors directly alleged for the first time that Cohen was being directed by Trump when he broke the law during the 2016 presidential campaign.

Democrats are suggesting Trump committed an impeachable offense and could be sent to prison when his term in the White House is over. The incoming chairman of the House Judiciary Committee, Rep Jerry Nadler, said Sunday the allegations, if proven, would constitute "impeachable offenses." Democratic Sen Chris Coons said Monday Trump could be indicted after he leaves office. White House officials, at the moment, still don't believe special counsel Robert Mueller's investigation into possible collusion will result in impeachment. Officials are also comforted by their belief that the campaign finance issue is not seen as enough to galvanize bipartisan support for impeachment.