U.S. Sen. Chuck Grassley said Friday that he would personally oppose Senate consideration of Supreme Court nominees in 2020 despite potential opposition from President Donald Trump and Republican leaders.

The senior senator, who is serving in his seventh six-year term, appeared on "Iowa Press" Friday, where he discussed the Russia investigation and trade, among other topics. He was joined by political reporters Kay Henderson, news director of Radio Iowa; Erin Murphy, Des Moines Bureau chief of Lee Enterprises; and David Yepsen, host of "Iowa Press."

The full program can be viewed here.

Grassley cited the "Biden Rule" — a guideline stemming from a speech given by then-Senator Joe Biden in 1992 — which contends that a vacancy on the Supreme Court in a presidential election year should be left open so the American people can have a say in who makes the decision.

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This rule was followed in 2016 when Grassley refused to hold hearings for Merrick Garland, then-President Barack Obama's nominee. If there is a vacancy in 2020, Grassley said he will follow the same rule, though he said both President Trump and Senate Majority Leader Mitch McConnell would not agree with him.

Henderson asked Grassley how he thinks history will write his role in blocking Garland from receiving a hearing.

"Well, I don't know what history will do and I don't care what history will do," Grassley said. "I'm just following what was established by the Biden Rule in 1986 and then emphasized by him in 1992.

"They set the pattern. I didn't set the pattern. But it was very legitimate that you can't have one rule for Democratic presidents and another rule for Republican presidents."

Henderson also questioned Grassley on his comments that Supreme Court justices planning on retiring should announce it immediately, amid rumors that Justice Anthony Kennedy plans to retire, as reported by USA Today.

"I'm not telling any Supreme Court justice what they should do, but there are rumors, last year and this year, that somebody might be retiring, and so I am trying to suggest to them the machinery of government," Grassley said. "If you want this president to replace it and you want a Republican Senate to look at you, you ought to have done it yesterday."

Grassley also discussed the investigation of Russian interference in the 2016 elections and Vice President Mike Pence's comments that Special Counsel Robert Mueller should wrap up the investigation.

"I would like to agree with Pence that it's gone on long enough," Grassley said. "It ought to be close to being ended, but if that's interpreted that you ought to shut it down whether it's ended or not, then I'd say no, this process ought to play out."

Murphy asked Grassley why he had a committee vote on legislation to protect Mueller from being fired, even though it is unlikely to ever see a floor vote or be signed by President Trump. Grassley said he tries to set the agenda for his committee in a bipartisan way when possible, saying the 31 bills that came out of his committee in 2015 and 2016 were all bipartisan.

When asked if he believes Mueller deserves that level of protection, Grassley said yes.

"It has a great deal to do with the constitutional role of Congress as oversight, and I wanted to protect that," Grassley said.

Shifting to Trump's policy on trade and its effect on Iowa agriculture, Murphy asked Grassley if a trade war could be a possible outcome of Trump's negotiation strategy.

"I believe that this president is doing something that a lot of other presidents never thought about doing, probably because they came from politics ... or from the military to be presidents of the United States," Grassley said. "We have a businessperson for the first time in the history of the country to be president. I think he brings a whole new approach."

Grassley went on to say that Trump thinks he can get a better deal for U.S. agriculture services and manufacturing. Grassley said if Trump is unsuccessful, the move could prove detrimental to Iowa agriculture, but if he is successful — and Grassley sees "a little bit of light at the end of the tunnel," he said — the U.S. will have better trade agreements.

"What do you say, though, senator, to an Iowa soybean farmer or a Kansas sorghum grower who sees prices falling out the bottom on their crops?" Yepsen asked. "I mean, what you're talking about, I understand the trade strategy, but there are a lot of people in agriculture who are hurting as a result of this."

Grassley said he wanted to make clear that he is very nervous about the approach, though he said right now he has some hope, citing progress in negotiations with China, which he said "would have never happened if Hillary Clinton was elected president."