Rep. Tom Allen (D-Maine) announced Tuesday that he will challenge Sen. Susan CollinsSusan Margaret CollinsOvernight Health Care: 3.6M signed up for ObamaCare in first month | Ryan pledges 'entitlement reform' next year | Dems push for more money to fight opioids Study: ObamaCare bills backed by Collins would lower premiums Right scrambles GOP budget strategy MORE, who is considered one of the most vulnerable Republicans, in 2008.

"Maine and America face unprecedented challenges," Allen said in this video announcing his run. "For the last six years, the Bush Administration, supported by a Republican Congress, has failed the American people."