Former defense secretary Robert Gates on Sunday pushed back against Senate Majority Leader Mitch McConnell’s call for the country to move on from Robert S. Mueller III’s report, arguing that Russian interference in U.S. elections remains an urgent issue.

McConnell (R-Ky.) last week declared “case closed” on Mueller’s report on Russian interference in the 2016 election. But in a wide-ranging interview on CBS News’s “Face the Nation,” Gates said the United States has “not reacted nearly strongly enough” to Russia’s “blatant interference in 2016.”

“The piece of the Mueller report about Russian interference is not ‘case closed,’” said Gates, a Republican who was defense secretary under presidents George W. Bush and Barack Obama. “And, frankly, I think elected officials who depend on honest elections to get elected ought to place as a very high priority measures to protect the American electoral system against interference by foreigners.”

In a phone call with Russian President Vladi­mir Putin earlier this month, Trump discussed the end of the Mueller investigation but did not raise concerns about the possibility of Russian interference in the 2020 campaign.

Gates said Sunday that was “a mistake.”

“I think he should’ve said, ‘We’ve had this discussion, the evidence is in and don’t ever do this again or there will be consequences for Russia,’ ” he told host Margaret Brennan. “I think he very much should have raised it with him.”

Gates’s comments come on the same day that Senate Minority Leader Charles E. Schumer (D-N.Y.) sent a letter to Secretary of State Mike Pompeo urging him to press Putin on the issue during their scheduled meeting this week in Sochi, Russia.

“During your meeting with Vladimir Putin, it is critical that you warn him that any action to interfere in our elections will be met with an immediate and robust response,” Schumer said in the letter. “President Trump’s approach to dealing with President Putin, especially on this vital issue, must change. I urge you to make absolutely clear to President Putin that interference in U.S. elections will not be tolerated.”

Trump has repeatedly given mixed messages on U.S. policy toward Russia, including during a Fox Business Network interview this month in which he suggested that it was a “rumor” that Russia had persuaded embattled Venezuelan President Nicolás Maduro not to flee the country — contradicting Pompeo’s statement on the matter.

Gates, who is chancellor of the College of William & Mary, speculated that Trump may be hesitant to confront Russia because of a “peculiar relationship with Putin” or because he “feels like any acknowledgment of Russian involvement in the 2016 elections somehow delegitimizes his being elected president.”

“I don’t know what the mix of motives are,” Gates said. “But the interesting thing is everybody around the president actually has a much more realistic view of the Russians, and that includes up on the Hill.”

He argued that in addition to sanctions, the Trump administration should consider “using some of our own capabilities to go back into Russia and, let’s say, inform the Russian people of the magnitude of corruption of Putin.”

“I think we can create more problems for him — we have the capabilities to do that,” Gates said.

Gates also criticized Trump’s handling of relations with Tehran, arguing that the president had erred in scrapping the Iran nuclear deal “in part because it ended up isolating us as well as the Iranians.”

“I believe the original agreement had some very deep flaws,” Gates said. “But once it was signed, I think it was a mistake to walk away from it. We should have then used various other pressures to address these other issues.”

Trump declared last week that former secretary of state John F. Kerry “should be prosecuted” for meeting with Iranian officials after leaving office in 2017. Gates dismissed that possibility on Sunday, telling Brennan, “Yeah, I mean this is not going to happen.”

“American politicians and former leaders talk to other leaders all the time,” he said.

Gates did, however, say that it would be “a mistake in judgment” to try to negotiate with a foreign government over policy issues after leaving office.

“I think trying to hold a negotiation, if you will, with a foreign leader when you’re out of power is a mistake . . . There’s only one president at a time,” he said.

Aaron Blake contributed to this report.