A new poll indicates Sen. Mark UdallMark Emery UdallSenate GOP rejects Trump’s call to go big on gun legislation Democratic primary could upend bid for Colorado seat Picking 2018 candidates pits McConnell vs. GOP groups MORE (D-Colo.) is vulnerable heading into 2014, dragged down in part by striking opposition to the health care law and a deeply unpopular president.

The survey, from Quinnipiac University, gives Udall just single-digit leads over all of his potential Republican opponents.

Republican District Attorney Ken Buck and businessman Jaime McMillan keep Udall's lead the tightest, down to three points for each. Against Buck, Udall takes 45 percent to Buck's 42 percent; the incumbent takes 43 percent to McMillan's 40 percent support.

Against the other four candidates, Udall's lead ranges from five to nine points.

More troubling may be the rise in his unfavorables from August. Then, 47 percent approved of the job he's doing, while 34 percent disapproved; now, voters are evenly split on his performance, 44-44 percent.

And now a plurality of voters, 47 percent, say he doesn't deserve reelection, a shift from August.

It seems that much of his drop may be due to an overall discontent with President Obama and his signature health care law. Obama gets his worst approval rating in any state or national Quinnipiac poll since he was elected in the new Colorado poll, with 59 percent of voters disapproving of his job performance.

Fifty-six percent of voters oppose the health care law.

And Udall's not the only one feeling that drag. Hillary Clinton, considered the likely leading Democratic presidential contender in 2016, now lags or ties all four possible GOP presidential contenders tested.

Christie now holds an eight-point lead over her, up from just one point in August, and Sen. Rand Paul (R-Ky.) leads her by three points. She ties Sen. Ted Cruz (R-Texas) at 44 percent support each, and slightly lags Rep. Paul Ryan (R-Wisc.), by two points.

The survey was conducted among 1,206 registered voters from Nov. 15-18 and has a margin of error of plus or minus 2.8 percentage points.