COLUMBUS — President Barack Obama’s approval rating with Ohio voters has dipped slightly, but Obama still leads major GOP challengers in possible 2012 match ups, according to a Quinnipiac University poll released Thursday.

“Voters are saying that they’re not overwhelmed by Mr. Obama but at this point they like him better than the alternatives,” said Peter Brown, assistant director of the Quinnipiac University Polling Institute.

Also, the poll finds that Ohio Treasurer Josh Mandel leads former state Sen. Kevin Coughlin of Cuyahoga Falls for the 2012 GOP U.S. Senate nomination, while incumbent Democratic U.S. Sherrod Brown holds healthy leads over both in general election matchups.

In the poll, 50 percent disapprove of how Obama is handling his job, while 46 percent approve, down from a May 19 poll which found 49 percent approval and 45 percent disapproval.

Voters split on whether the president deserves a second term, with 47 percent “no” and 46 percent “yes.”

In the scramble for the 2012 GOP presidential nomination, “don’t know” is the big leader at 28 percent. Here’s the rest:

• Former Massachusetts Gov. Mitt Romney, 16 percent;

• Former Alaska governor and 2008 GOP VP candidate Sarah Palin, 15 percent;

• U.S. Rep. Michele Bachmann of Minnesota, 11 percent;

• Texas Gov. Rick Perry, 8 percent.

No other candidate tops 6 percent.

Romney comes closest in match ups with Obama, with the president leading, 45-41 percent.

Incumbent Democrat Brown beats Mandel, 49-34 percent and bests Coughlin, 50-32 percent.

The poll was conducted from July 12 to Monday, July 18 and is based on interviews with 1,659 registered voters done by live interviewers on land lines and cell phones. Overall, the poll has a margin of error of plus or minus 2.4 percentage points.

The survey included 563 Republicans and GOP only questions have a margin of error of plus or minus 4.1 percent.