WASHINGTON, D.C. – President Barack Obama is not on the ballot this year, or in 2016 for that matter, which may be a good thing for Democrats. Even though the president's approval rating in Ohio has dropped again – to 36 percent – he doesn't seem to be hurting his party's presumptive presidential front-runner.

Hillary Clinton still could beat the most likely Republican challengers, in other words, according to a new poll of Ohio voters released this morning by Quinnipiac University.

A more perplexing problem may exist for U.S. Sen. Rob Portman, an Ohioan on the state ballot – and possibly the national one -- in two years. Portman is nearly four years into his term, yet a full third of Ohio voters say they don't know enough about his job performance to rate it.

The good news for Portman, a respected Republican lawmaker in Washington and one who says he might consider running for president, is that he has a higher approval rating, at 40 percent. His disapproval rating is 28 percent in this newest Quinnipiac poll.

But the share of Ohio voters who don't know enough about him is 32 percent, slightly higher than the 30 percent and 29 percent "don't know" ratings that Ohioans gave him in other Quinnipiac surveys conducted since last June.

Ohio U.S. Sen. Sherrod Brown, a Democrat who doesn't face reelection until 2018, has held steady with a 49 percent approval rating, the same as in the last Quinnipiac poll on May 15.

Brown's disapproval is at 32 percent, a slight improvement since May – and a 6-point improvement since June 2013.

Interestingly, the share of Ohioans who say they know too little about Brown to rate him has grown from 16 percent in June 2013 to 19 percent today. The poll does not address why, and the reason could be the same for both Brown and Portman, even though Portman's numbers in this category are much higher.

Congress has passed few significant bills this year, so the spotlight has faded from either senator. More than a year has passed since Portman made waves by saying he supports gay marriage, contrary to the position of most in his party. Both Portman and Brown get regular press coverage in Ohio and elicit strong feelings from readers on Internet news sites, but the general public's focus may be elsewhere in a year in which neither Portman nor Brown is running.

As for Obama, only 36 percent of Ohio poll respondents said they approve of his performance, while 59 percent said they disapprove. Five percent said they did not know.

The negative rating is close to Obama's all-time low in Ohio and the other eight states in which Quinnipiac polls regularly, said Peter Brown, assistant director of the Quinnipiac Poll.

Obama's lowest rating in Quinnipiac surveys, performed regularly in Ohio and other key electoral states, was 61 percent last November.

"The bad news for Democrats is that President Obama's approval rating in Ohio is close to his all-time, all-state low," said Brown. "The good news for the party is that the president doesn't appear to be hurting the Democrats' consensus front-runner for 2016, former Secretary of State Hillary Clinton."

Support for any candidate will vary along party lines, but only 74 percent of Democratic voters in this survey said they approve of Obama's job performance, a rating Brown called "anemic, at best."

Ohio Republican approval of Obama is at 4 percent.

The new poll shows that if a one-to-one matchup were held in Ohio today, Clinton would beat Republican U.S. Sen. Rand Paul of Kentucky by 46 to 42; Ohio Gov. John Kasich by 47 to 40; former Florida Gov. Jeb Bush by 48 to 37, and New Jersey Gov. Chris Christie by 46 to 37.

Forty-six percent of Ohio voters said they had a favorable opinion of Kasich, to 30 percent who view him unfavorably. Twenty-one percent said they had not heard enough about him to give an answer.

Fifty-two percent of Ohio voters in the poll said they had a favorable opinion of Clinton and 43 percent said they had unfavorable views. But there is no question that voters easily define her. Only 5 percent said they had not heard enough or don't know enough about her to give an opinion, and 1 percent refused to answer the question.

The Quinnipiac Poll, affiliated with Quinnipiac University in Connecticut, surveyed 1,366 registered Ohio voters from July 24 to July 28, reaching them by land lines and cell phones. The poll's margin of error is 2.7 percentage points.