Senate Judiciary Chairman Chuck Grassley is amping up the panel’s investigation into Russian interference in the 2016 presidential election, weighing whether to issue subpoenas for Donald Trump Jr. and former campaign chairman Paul Manafort, Bloomberg News first reported Monday.

Grassley’s committee is conducting its probe in addition to the Senate Intelligence Committee and special counsel Robert Mueller’s investigations, which some– including Senate Majority Whip John Cornyn — have said they feel is inappropriate.

While the move has received some pushback, Grassley stands by his decision to push forward with the investigation alongside Ranking Member Dianne Feinstein, arguing it’s their duty to look into whether there was any sort of obstruction of justice.

“This is what Chuck Grassley does,” Grassley said in his interview with Bloomberg.

The Iowa Republican argued possible collusion is cause for bipartisan concern, adding the White House is aware it’s their job to look into the matter.

“They may be new to town, but they surely recognize what Chuck Grassley’s reputation is. And if they don’t know it, they’ve been told, I bet, a hundred times,” he continued in the interview. “I think I’ve got a pretty good reputation for being what I call an equal-opportunity overseer.”

According to Grassley, neither top Republicans nor the Trump administration has reached out in an attempt to halt the probe.

“I’ve had no face-to-face contact with anybody, I’ve had no phone calls from anybody, not only my colleagues but not from the White House either,” he told The Hill in an interview.

South Carolina Sen. Lindsey Graham praised Grassley’s efforts, saying he is loyal to the party but concerned with the greater good of the country.

“He’s a good conservative, but he loves the institution, and he’s got that Iowa sense of fairness,” Graham told Bloomberg. “He doesn’t go pick a fight, but if you get in a fight with him you’ve got a worthy opponent. I think the more you stonewall him, the worse it gets.”

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