Air Force Reserve Col. John Tree (D) jumped into the primary to challenge Rep. Robert Dold (R-Ill.) this week.

“I’m very disappointed in Congressman Dold,” Tree said in a statement about his candidacy. “He had opportunity this past summer to do what was right for America. He didn’t display the moral courage and the leadership we need and all of us Americans are looking for.”

Dold is one of the most vulnerable GOP House Members following a Democratic-led redraw of the state’s Congressional map. Democrats shifted Dold’s base of Winnetka out of the district and made the already Democratic district even more so under the new lines.

Tree is the third Democrat to enter the race against the GOP freshman. Former MoveOn.org organizer Ilya Sheyman and businessman Brad Schneider are already running for the Democratic nomination.

Dold won his first term last year in an open-seat race with 51 percent of the vote.