A poll conducted on behalf of Rep. Tom Cotton’s campaign found the Arkansas Republican with a 4-point lead over Democratic Sen. Mark Pryor — within the margin of error for the survey.

In one of the GOP’s top pickup opportunities in 2014, Cotton led 45 percent to 41 percent, with 15 percent of those surveyed undecided.

The poll of 600 likely voters was conducted by GOP firm OnMessage Inc. on Oct. 15-17. The margin of error was 4 points.

Pollster Wes Anderson argues in the polling memo that Pryor is vulnerable because of his support of President Barack Obama and the president’s health care law. The poll found that about 6 in 10 voters held an unfavorable view of Obama and opposed Obamacare.

Meanwhile, the Pryor campaign launched a new TV ad this week that hangs the government shutdown on Cotton. With the Republican brand taking a hit nationally in the polls in the wake of the shutdown, the ad ties Cotton to “a small group of reckless congressmen” that led the effort.

The race is rated a Tossup by Rothenberg Political Report/Roll Call.