Former U.N. Ambassador John Bolton, a mainstay of past Republican administrations, doesn’t think Donald Trump colluded with the Russians. But if the Russians meddled in U.S. elections, they must be dealt with.

In a powerful 20-minute speech to a few thousand people at the Western Conservative Summit in Denver Friday night, Bolton said he hasn’t seen evidence to convince him Trump’s campaign was complicit.

“The evidence is unmistakable Russia tried to interfere in our election,” Bolton said. “I think there’s no evidence the Trump campaign tried to collude with the Russians.”

Holding his bent thumb and index finger about an inch apart, he said. “These are two different issues.” Applause ensued.

Bolton speculated that Trump delivered a message during meetings with Vladimir Putin at the G20 Summit in Germany on July 7.

“We believe efforts to interfere in American elections constitutes an existential threat to the idea of America,” Bolton said. “We are an exceptional country because we are the only country founded on the idea of individual liberty and control over our government.

“And when the Constitution is interfered with, especially by foreigners, we consider that an act of war.”

He said Trump could keep America safe, “but he’s hamstrung by the national security bureaucracy.”

Bolton gave dire warnings about the risks of North Korea, Iran or terrorists being able to attain ballistic nuclear weapons. Bolton raised the possibility of such a device being brought into a port anywhere in the world on a steamer, or smuggled in pieces across America’s southern border and reassembled in a U.S. city.

“The president, I think, understands the nuclear threat,” Bolton said. “It’s an imminent danger for the United States. I think he has resolved to ensure that neither Iran or North Korea or anybody else gets nuclear weapons capability.”

He was critical of Obama’s 2015 nuclear deal to put Iran on a shelf, but Bolton said it’s not working, citing evidence that Iran is still trying to up its nuclear potential. He said it unfroze $150 billion in assets Iran could use for its acquisition.

“This deal Obama signed isn’t constraining Iran from getting nuclear weapons,” Bolton said. “It’s facilitating Iran getting nuclear weapons.”