(CNN) - She's still ahead of the competition, but a new poll in an important presidential battleground state indicates that Hillary Clinton's numbers have slightly deteriorated over the past couple of months.
According to a Quinnipiac University survey of Ohio voters, Clinton remains in the lead over eight potential Republican opponents in hypothetical 2016 presidential election showdowns, but her margins have shrunk.
"Her lead over most of them has dropped considerably since Quinnipiac University surveyed Ohio voters in February," said Peter A. Brown, assistant director of the Quinnipiac University Poll. "Still Ms. Clinton has the best favorability rating of the group."
The former secretary of state, senator from New York and first lady, has said she'll decide by the end of the year if she'll launch a second bid for the White House. And most of the potential GOP presidential candidates questioned in the survey have also indicated they'll make their decisions sometime after November's midterm elections.
The poll, released Thursday, indicates Clinton leading former Florida Gov. Jeb Bush 48%-39% among registered voters in Ohio. That's down from a 51%-36% lead in February. Clinton leads Sen. Marco Rubio of Florida 47%-40%, down from 50%-36% three months ago. And she tops Sen. Rand Paul of Kentucky 49%-41%, down from 51%-38%.
According to the survey, Clinton's ahead of New Jersey Gov. Chris Christie 46%-38%, down from 49%-36% in February. She's ahead of Rep. Paul Ryan of Wisconsin 48%-41%. That's slightly down from her 49%-40% advantage over the 2012 GOP vice presidential nominee three months ago. And she tops Sen. Ted Cruz of Texas 51%-37%, down from 51%-34%.
And Clinton has a 47%-42% edge in Ohio over the state's governor, John Kasich, down from 51%-39% in February. She also has a 49%-41% lead over former Arkansas Gov. Mike Huckabee. The 2008 Republican presidential candidate was not tested in Quinnipiac's February poll.
Ohio plays a crucial role in campaign politics. It's a must win battleground state in presidential elections and was the state that put George W. Bush over the top in his 2004 re-election. In modern times, no Republican has ever been elected to the White House without carrying the Buckeye State.
The slight deterioration of Clinton's lead in Ohio matchups is opposite of what Quinnipiac polling found in Florida, another crucial battleground state. A Quinnipiac poll conducted in the Sunshine State earlier this month indicated Clinton's leads over Bush, Rubio, Paul, Christie, Ryan and Cruz had slightly increased since the beginning of the year.
A national survey conducted earlier this month indicated that Clinton was overwhelming frontrunner in the race for the 2016 Democratic presidential nomination, but that her support had slightly deteriorated since the beginning of the year.
According to the CNN/ORC International poll, 64% of Democrats and independents who lean towards the party said they most likely would support Clinton, down six percentage points from January, when seven in ten said they'd back Clinton. Nineteen percent said they are likely to support a Democratic presidential candidate who's more conservative than Clinton, up four points from January, with 13% saying they'd back a candidate more liberal than Clinton, up three points from the beginning of the year.
One caveat: With the start of the 2016 primary and caucus calendar still more than a year and a half away, polls at this early stage in a presidential cycle are often influenced by name recognition.
According to the Quinnipiac poll, Buckeye state voters have a 53%-43% favorable opinion of Clinton. Her numbers on this question are basically unchanged from last June. Favorite son Kasich stands at 47% favorable and 29% unfavorable. The ratings for the other possible 2016 Republican White House hopefuls are: Bush (32%-38%); Christie (36%-36%); Paul (38%-29%); Cruz (24%-26%); Huckabee (37%-31%); Ryan (39%-31%); and Rubio (31%-19%).
As for the current resident in the White House, 39% of Ohio voters say they approve of the job President Barack Obama's doing, with 58% saying they disapprove. The President stood at 40%-55% in February.
The Quinnipiac University poll was conducted May 7-12, with 1,174 registered voters in Ohio questioned by telephone. The survey's overall sampling error is plus or minus 2.9 percentage points.