President Obama and Sen. Sherrod BrownSherrod Campbell BrownSenate Dems to Mnuchin: Don't index capital gains to inflation Trump on collision course with Congress on ZTE Pa. health secretary: 'Sustainable funding' needed to attack opioid crisis MORE (D-Ohio) could be vulnerable to challenges in Ohio but currently lead all challengers, according to a poll released Thursday morning by Quinnipiac University.

Obama's job approval rating sits at 46 percent, with 50 percent disapproving. A bare plurality believe he doesn't deserve a second term, at 47 percent to 46 percent who would vote for him.

The president so far leads all the likely Republican candidates, however. He holds a narrow 45-41 percent lead over former Massachusetts Gov. Mitt Romney, but tops former Alaska Gov. Sarah Palin 51 percent to 35, beats Rep. Michele BachmannMichele Marie BachmannBachmann won't run for Franken's Senate seat because she did not hear a 'call from God' Billboard from ‘God’ tells Michele Bachmann not to run for Senate Pawlenty opts out of Senate run in Minnesota MORE (R-Minn.) 49 percent to 36 and leads Texas Gov. Rick Perry 47 percent to 35.

“Ohio voters may not be wild about President Barack ObamaBarack Hussein ObamaTrump: Police 'have every right' to protest Chicago mayor To woo black voters in Georgia, Dems need to change their course of action 2018 midterms: The blue wave or a red dawn? MORE, but at this point they appear to like his potential Republican challengers less, and in some cases a lot less,” said Peter A. Brown, assistant director of the Quinnipiac University Polling Institute. “His middling job and reelection ratings show that there may be a potential opportunity to defeat President Obama in 2012 in Ohio, but for that to occur the GOP will have to nominate a candidate that can capture the public’s imagination to a degree not yet evident.”

The Buckeye State, always a bellwether, could determine control of both the White House and the Senate in 2012. While it loses two electoral votes due to reapportionment, Ohio still has 18, making it one of the largest swing states in the country.

Obama won there with 51 percent of the vote in 2008. Since then the Rust Belt state's economy has continued to struggle and the Democratic-heavy areas of northern Ohio have continued to lose population, making the state a bit more Republican demographically. But these polls indicate Obama and Brown are in a better position for reelection here than Democrats are in some other swing states.

Only against the well-known and polarizing Palin does Obama cross the 50 percent threshold. The other candidates have lower name recognition, which helps to explain Obama's lead — and the higher number of undecided voters in those head-to-head match-ups.

Brown remains more popular than Obama in the state, according to the poll. Ohio voters approve, by 49 to 30 percent, of the job he is doing and say, 47 to 33 percent, that he deserves to be reelected. He leads his most likely challenger, Ohio Treasurer Josh Mandel, by 49 to 34 percent, and another challenger, state Rep. Kevin Coughlin, by 50 to 32 percent.

“Sen. Sherrod Brown has very healthy leads over his potential challengers with 16 months to go before the election," says Quinnipiac's Brown. "He is just around the magic 50 percent threshold that many see as the dividing line for incumbents to ensure their reelection,” said Brown.

Mandel, whose huge $2.3 million haul in the last three months has put him on the radar screen as a possible heavyweight contender, leads Coughlin by a wide 35-12 percent edge among Republican primary voters.

The poll of 1,659 registered voters was conducted from July 12-18 with a margin of error of plus or minus 2.4 percentage points. The survey includes 563 Republicans with a margin of error of plus or minus 4.1 percent.