Jeh Johnson, secretary for the Department of Homeland Security in the Obama administration, said Tuesday the Supreme Court's ruling on presidential immunity is a "setback to our constitutional order."

"This is, to me, an unbelievable decision," Johnson, a Democrat, told MSNBC's "Morning Joe." "And, in my view, it's a setback to our constitutional order."

In a 6-3 decision Monday, the Supreme Court ruled for the first time that former presidents have some immunity from prosecution regarding official acts while in office. The decision means Trump's case in Washington, D.C., on federal charges of trying to subvert the 2020 election results likely won't go to trial before November's election.

"I took constitutional law 45 years ago," Johnson said. "I think I must have missed the lesson where my teacher said, 'There's this provision in the Constitution that says, presidents have criminal immunity from criminal liability.' "

The majority opinion by Chief Justice John Roberts found Trump is "absolutely immune" from prosecution for alleged conduct involving discussions with the Justice Department. He also is "at least presumptively immune" from allegations that he tried to pressure Vice President Mike Pence to reject congressional certification of Joe Biden's victory on Jan. 6, 2021. Prosecutors can try to make the case that Trump's pressure on Pence still can be part of the case against him, Roberts wrote.

The high court directed the trial court to analyze one of the more striking allegations in the indictment — that Trump participated in a scheme to enlist fake electors in battleground states won by Biden who would assert that Trump won. U.S. District Court Judge Tanya Chutkan will undertake that task.

"The framers of the Constitution knew how to write immunity into the Constitution, the speech and debate clause, which gives immunity to legislators for things that they say," Johnson said. "No such provision exists for the president. If this doctrine has existed all along for the last 235 years, then [Gerald] Ford didn't need to pardon [Richard] Nixon.

"When Nixon said to David Frost in 1977 in an unguarded moment, 'When the president does it, it is not illegal,' we were all shocked, we were appalled. It was an extreme statement. Turns out [six] justices of the current Supreme Court agree with that."