A medical researcher announced Thursday that he is running against GOP Rep. Dana Rohrabacher, who Democrats view as particularly vulnerable in 2018.

Rohrabacher’s re-election race is one of the contests where the investigation into Russian interference in the 2016 elections could be a more pertinent campaign issue, since Rohrabacher is a vocal supporter of bolstering relationships with Russia.

Dr. Hans Keirstead is an expert in stem cell research and CEO of the biomedical company AIVITA. National Democrats view Keirstead as a strong challenger to unseat the California Republican. Keristead has also been working with 314 Action, a group promoting people in scientific fields running for office.

“Through my career in medicine and as an entrepreneur, I’ve dedicated my life to saving and improving people’s lives — working to find cures for diseases previously thought incurable and being held accountable for those result,” Keirstead said in a statement. “I’m running for Congress because I believe that innovative thinking and a people-first attitude matter to the constituents of this district.”

Rohrabacher represents a district in Orange County that is rated Lean Republican by Inside Elections with Nathan L. Gonzales. Rohrabacher won re-election to a 15th term in 2016 by 17 points. But Democratic presidential nominee Hillary Clinton won the district by nearly 2 points, according to Daily Kos Elections.

Keirstead joins Realtor Harley Rouda and real estate broker Boyd Roberts in the Democratic field. Rouda showed some early fundraising power, raising $100,000 in the first 12 days of his campaign.

Rouda has also slammed Rohrabacher, who supports President Donald Trump, for his comments on Russia. The New York Times reported in May that the F.B.I. warned Rohrabacher that Russian spies were attempting to recruit him. House Majority Leader Kevin McCarthy, R-Calif., seemingly joked that Rohrabacher and Trump were the two politicians paid by Russian President Vladimir Putin, the Washington Post reported last month as well. 

Rouda slammed Rohrabacher following the Washington Post report, even writing a letter to the FBI encouraging the agency to investigate the California Republican.

“Reports in the press indicate that there is already an investigation into the Russia ties of Trump’s associates, but I believe the public needs to know definitively whether Congressman Rohrabacher has any financial ties to the Russian regime,” Rouda wrote.

But Rohrabacher has dismissed concerns about his Russian sympathies.

“I was hard-core anti-communist and anti-Soviet; I was never anti-Russian,” Rohrabacher told the Washington Post at the end of May. “The very same groups of people who are unrelenting in their hostility today wanted to be friends with Russia when it was run by atheistic communist dictators.”