Former national security adviser H.R. McMaster on Monday said he wouldnt serve in a second Donald Trump administration if the Republican presidential nominee wins in November.

McMaster joined the Trump White House in early 2017 to replace Michael Flynn, who resigned from the national security adviser role after it became known that he had lied to then-Vice President Mike Pence about his dealings with then-Russian Ambassador Sergey Kislyak.

But McMaster left the administration a little over a year later. During his tenure, he often appeared at odds with Trump. For instance, in 2017, McMaster said there was incontrovertible evidence that Russia tried to interfere in the 2016 presidential election a statement that appeared to irk Trump, who called out McMaster on his Twitter account .

In an interview with CNN s AC360, McMaster said he wouldnt work for Trump again if the former president secured reelection.

I would work in any administration where I feel like I can make a difference, but Im kind of used up with Donald Trump, McMaster said.

McMaster added that he also wouldnt serve under Vice President Kamala Harris if she won the race, citing policy differences.

Meanwhile, when asked if he believes former White House chief of staff John Kellys recollections that Trump made disparaging comments about wounded service members, calling them losers, McMaster said those words dont appear consistent with what hed expect from the former president. Trump has also disputed Kellys account.

I wasnt there, McMaster said. I was gone by that time. It sounded out of character to me. I never heard the president say anything like that, that bad.

When pressed about Trumps attacks on the late Sen. John McCain (R-Ariz.), though, McMaster conceded that Trump can often be very offensive.

Hes an extremely disruptive person, McMaster told CNNs Anderson Cooper . I saw it as my job not to try and constrain him, but to help him disrupt what needed to be disrupted.

During his 2016 presidential campaign, Trump said McCain is not a war hero. McCain, who served in the Navy, spent over five years in a North Vietnamese prison, where he was tortured.

He was a war hero because he was captured, Trump said. I like people who werent captured.