President Donald Trump said Thursday that he will be swapping out national security adviser H.R. McMaster for former U.N. ambassador John Bolton, known Russia hawk, come mid-April.

Trump himself has not consistently taken a strong stand against what other administration officials have condemned as the Kremlin’s malign activities, including interference in the 2016 election. Most recently, he drew criticism for calling Russian President Vladimir Putin and congratulating him in what many described as a rigged election.

On Wednesday, Trump pushed back on criticism, tweeting that he wanted t o improve relations with Russia and focus on areas of mutual interest. He cited Syria, Ukraine, North Korea, and the fight against the Islamic State.

His new national security adviser could take a more skeptical approach. Here’s a look at some of Bolton’s statements regarding Russia and its leader Vladimir Putin over the last several years.

He continued: “For Trump, it should be a highly salutary lesson about the character of Russia’s leadership to watch Putin lie to him. And it should be a fire-bell-in-the-night warning about the value Moscow places on honesty, whether regarding election interference, nuclear proliferation, arms control or the Middle East: negotiate with today's Russia at your peril.”

In the same Telegraph piece, Bolton described Russia’s attempts to undermine the U.S. election as “a casus belli , a true act of war, and one Washington will never tolerate.”

“Russia, China, Syria, Iran, North Korea. These are regimes that make agreements and lie about them,” he said. “A national security policy that is based on the faith that regimes like that will honor their commitments is doomed to failure.”

In a recent Fox interview, Bolton warned more broadly against easily buying into promises from regimes like Russia and North Korea.

“Trump got to experience Putin looking him in the eyes and lying to him, denying Russian interference in the election,” Bolton wrote in the Telegraph. “It was predictable Putin would say just that, as he has before (offering the gratuitous, nearly insulting suggestion that individual hackers might have been responsible).”

Bolton warned Trump about the perils of negotiating with Russia in July 2017, after the president met with Putin in person for the first time at the G-20 summit.

Bolton has long advocated for punishing Russia over actions that do “real damage.” In 2013, after Russia gave former CIA analyst Edward Snowden asylum, Bolton said: “I think in order to focus Putin’s thinking, we need to do things that cause him pain as well. And while I know that not having a chance to have a bilateral meeting with his buddy Barack Obama will cause Putin to lose sleep, it’s not damaging Russian interests.” He did not see then-President Barack Obama’s decision to cancel a meeting with Putin as a legitimate punishment. “Canceling this meeting has all the impact on Putin of Obama fluttering his eyelids,” he said. “It’s purely symbolic.”

Bolton offered a similar assessment in December 2016 after Obama expelled 35 Russian intelligence operatives, closed two diplomatic compounds, and levied sanctions on Russian intelligence services and business entities. The former U.N. ambassador said the measures would not “have much impact at all.” “If you make them feel pain, and others feel pain, then the possibility of deterring future conduct like this increases,” he said. “It is an attack on our constitutional system. It is not enough to say, and people should be very careful about this, to say, ‘well, it didn't actually have an impact on the election,’” Bolton said. “You know, the fact that Russian efforts were incompetent or insufficient shouldn't make us feel better.”

Bolton advised the administration to “abrogate” the New START (Strategic Arms Reduction) Treaty that took force in 2011. Echoing comments made by Trump, Bolton slammed the treaty for giving Russia “a decided advantage that we didn’t have to give away, but the Obama administration did.” “The next step in the bilateral relationship with Russia is for this administration to abrogate the New START Treaty so that we have a nuclear deterrent that’s equal to our needs to prevent future conflict,” he said at the 2017 Conservative Political Action Conference. “That would be a signal to Vladimir Putin.” And he advised the president to threaten Putin to comply with the 1987 intermediate-range nuclear forces (INF) treaty, meant to limit the development of certain missiles. “President Trump should say to Vladimir Putin, ‘you either bring Russia back into compliance with the INF Treaty or we're gonna get out of that one, too,’” he said to applause.

More recently, Bolton urged “a very strong response” to Russia’s poisoning of ex-spy Sergei Skripal in the U.K. “This is unacceptable conduct,” he said on Fox News. He said the expulsion of 23 Russian diplomats by the U.K. “was the right thing,” but would not describe it as a “strong response.” “The response needs to be such that we begin to create, in Vladimir Putin’s mind, deterrence theories that he will understand if he undertakes this again the cost that Moscow will bear will be significantly greater. That’s how deterrence works,” he said.