The Wisconsin Republican and former secretary of State top a new Iowa Poll.
The president's approval rating has plunged to 41 percent with voters aged 18-29.
Christie leads Clinton in the key swing state by 43 to 38 percent, according to the poll.
Anger over the shutdown could be enough to push the GOP out of power, according to Public Policy Polling.
According to a new survey, 65 percent of Democrats or liberal-leaning independents say they would back Clinton.
Hispanics in the U.S. lean strongly Democratic overall, with only moderate differences based on their place of birth, poll shows.
The governor drew 21 percent support in a poll of Republican primary voters, while backing for Sen. Marco Rubio plunged.
The poll from Latino Decisions shows that even GOP champions of immigration reform trail top Democrats.
Markey leads 54 to 41 percent, with 4 percent undecided in the Boston Globe poll.
The pollster is trying to determine why its data on likely voters "skewed" toward Mitt Romney.