Artwork for a billboard that is slated to go up soon on the Heartland Bank building on High Street in Columbus.

A recent survey of likely Ohio voters by Gerstein Bocian Agne strategies shows U.S. Sen. Rob Portman, R-Cincinnati, is hurt badly by the endorsement of Republican presidential nominee Donald Trump in Portman’s re-election race against former Ohio Gov. Ted Strickland.

A memo for the survey dated July 21 said that the U.S. Senate race between Strickland is a statistical dead heat, with Portman leading Strickland 48 percent to 46 percent with 6 percent undecided and a 3.5 point margin of error.

The survey for Project New America was conducted between June 29 and July 6 with phone interviews of 920 likely voters including 39 percent self-identified Democrats, 32 percent self-identified Republicans and 29 percent self-identified independents or third party members.

Portman’s fortunes in the race could be tied to Donald Trump’s, the memo said, with a majority of voters saying they would be less likely to support Portman because he endorsed Trump – including nearly a quarter of current Portman supporters.

Earlier this month in the New York Times, top Trump advisor Paul Manafort said, “We are working very closely with Rob Portman” and “we’re running our campaigns together.”

While Portman leads the Senate race by two percentage points (within the survey’s margin of error), results show that lead will be in jeopardy if voters begin to associate Portman with Trump. A majority of voters, at 52 percent, said that a Trump endorsement from Portman would make them less likely to support him for Senate, including 38 percent said it would make them much less likely to support him.

More importantly, the memo said, such an endorsement would hurt Portman with some people who are currently supporting him. Twenty-four percent of Portman voters say that their candidate endorsing Trump would make them less likely to support him. That is more than 11 percent of the entire electorate, the memo noted, a potentially massive vote shift away from Portman.

The small share of undecided voters would be even more persuaded to vote against Portman, it said, with 47 percent saying it would make them less likely to support the Republican and just 16 percent saying it would make them more likely.

The survey also found that Portman is buoyed in part by a 13-point advantage among white voters. But Strickland’s performance among black voters (who constitute 11 percent of the likely electorate) is very strong, with Strickland leading Portman by an 81 percent to 11 percent margin, the memo said.