Rep. Devin Nunes (R-CA) attends a House Ways and Means Committee markup of the Republicans tax reform plan titled the Tax Cuts and Jobs Act., on Capitol Hill in Washington, D.C., Nov. 9, 2017.

Rep. Devin Nunes, R-Calif., could face an uphill battle in 2020 due to a possible ethics probe and a Democratic challenger who is receiving a surge in fundraising.

Nunes, the ranking member on the House Intelligence Committee, is known for his ardent defense of President Donald Trump amid the ongoing impeachment inquiry, which aims to reveal whether Trump used military aid to pressure Ukraine into an investigation of Hunter Biden's dealings with the country.

Nunes has called the impeachment inquiry "a show trial not meant to discover the facts." He has tried to allege that Ukraine intervened in the 2016 election, which impeachment witness and former National Security Council official Fiona Hill has called a "fictional narrative."

But Nunes could have a conflict of interest in the inquiry. Lev Parnas, a recently indicted associate of Trump's personal lawyer Rudy Giuliani, is reportedly willing to tell Congress that Nunes met Ukrainian officials in Vienna last year to discuss digging up dirt on Democratic presidential candidate Joe Biden. When questioned on Fox News about whether he had visited Vienna, Nunes would not directly answer the question.

Records show that Nunes spent $57,000 last year on a trip for him and his staff to Europe between Nov. 30 and Dec. 3.

Nunes has threatened to sue CNN and the Daily Beast, two media outlets that reported on the story. He could face a possible House ethics investigation into the allegations, which could hurt him in his 2020 reelection campaign.

Nunes' 2020 challenger, Democrat Phil Arballo, claims that his campaign has raised nearly $300,000 since public impeachment hearings began this month. Arballo, a Hispanic small business owner, has said that he has received a "tremendous groundswell of grassroots support."

“I think people are really understanding from this last week and a half what Devin Nunes is really about and that’s about serving in his best interest and the best interest of this president,” Arballo said on MSNBC Sunday. Arballo has tried to paint Nunes as an out-of-touch career politician.

Nunes, a former dairy farmer, has represented California's 22nd district since 2003, which is centered in the San Joaquin Valley — California's largest agricultural region.

In 2018, Nunes won re-election at just 52.7%, beating out Democratic challenger and Fresno County Prosecutor Andrew Janz who received 47.2%.

Nunes has seen controversy before. He was forced to recuse himself from the investigation of collusion between Russia and the Trump campaign, due to his close ties to the White House. He has also tried to sue a satirical cow on Twitter for defamation.