WASHINGTON — (CNN) Hillary Clinton has a narrow advantage over Donald Trump in the swing state of Ohio, according to a new poll released Monday.

The Monmouth University poll finds Clinton up four points on Trump among likely Ohio voters, 43% to 39% — within the survey’s 4.9-point margin of error.

Additionally, Libertarian candidate Gary Johnson is getting substantial support in the state, with 10% saying they’ll vote for him, while less than 1% say they will vote for Green Party candidate Jill Stein.

Clinton’s lead is consistent with most post-convention polling of the Buckeye state, where Clinton is generally shown leading by mid-single digits.

The Monmouth poll found Clinton and Trump performing about the same with voters of their respective parties, which suggests there is growing party unity as the election approaches and both candidates continue to work to shore up their base.

Trump is backed by 83% of Republicans, and Clinton gets the support of 88% of Democrats.

Meanwhile, independents back Trump and Clinton in equal measure — 35% — with a full 20% saying they’ll go for Johnson.

In demographic terms, Clinton and Trump are both outperforming their predecessors, Barack Obama and Mitt Romney, among the groups that those candidates lost in 2012.

Clinton leads Trump among black, Hispanic and Asian voters 72% to 10%. But in 2012, Obama beat Romney in that group by a larger margin, 84% to 14%.

Conversely, Clinton is outperforming Obama among white voters. She draws 37% of their support to Trump’s 45% — better than Obama’s loss to Romney in that group by 16 points.

This is partly because while Trump leads comfortably among white men, 52% to 28%, he is losing white women to Clinton, 38% to her 46%.

The Monmouth University poll also found that Ohio’s governor, John Kasich, has not hurt his standing among his state’s Republicans, despite his public refusal to support Trump as the GOP nominee.

The survey found that 38% say they think more highly of Kasich for his position, while just 17% say they think less highly of him.

Forty-four percent said his decision had no impact.

Lastly, the Montmouth poll found incumbent GOP Senator Rob Portman leading the former Ohio governor Ted Strickland, his Democratic challenger, by 48% to 41%.

The race could have major implications for control of the upper chamber of Congress.

The Monmouth poll was conducted between August 18 and 21, and sampled 402 Ohio residents likely to vote in November.

It has a margin of error of 4.9 points.