The poll comes after Romney said "circumstances can change" when asked about 2016.
Congress’s low approval rating could drive more voters to the polls in November.
Clinton leads Warren by 38 points among the state's likely Democratic voters.
Voters are on pace to give lawmakers their lowest reelection measure in 20 years.
Quinnipiac University survey shows Rep. Gardner (R) leading Sen. Udall (D) 44 to 42 percent.
She crushes potential Dem competitors in early states but is vulnerable to GOP matchups.
Rand Paul gets highest numbers in both states among Republicans.
A Gallup poll found 91 percent of people are familiar with Clinton.
Fifteen percent approve of the way Congress is handling its job, according to a new poll.
Hillary Clinton also sweeps the potential 2016 Democratic field for president.