McMaster told ABC News Chief White House Correspondent Jonathan Karl and Political Director Rick Klein that he believed the administration "affected the most significant shift in U.S. foreign policy since the end of the Cold War" during his tenure, including "a competitive approach to China rather than a policy of cooperation (and) engagement."
But as for its stance regarding Russia, McMaster described Trump as out-of-sync.
"We had significant shifts on our approach to Russia, which, of course, is completely disconnected from the president's public statements about Russia, which is frustrating and counterproductive," he said on the "Powerhouse Politics" podcast.
Trump's political career, from the launch of his presidential run five years ago through these final days of his first term, has been marred by criticism of his relationship with Russia, including his open admiration of President Vladimir Putin, questions about his personal interactions and business dealings with Russian nationals and the allegation that his campaign colluded with the nation to interfere in the 2016 election. On the final point, special counsel Robert Mueller did not find "sufficient to charge any member of the campaign with taking part in a criminal conspiracy," related to election interference.
During Wednesday's interview, McMaster addressed continued Russian election interference, arguing that Trump should be "taking credit" for the strides the U.S. took following the 2016 cycle, rather than his choice to "raise doubts about our electoral process."
"We got exponentially better at protecting our election process, exponentially better at countering this Russian campaign of disruption, disinformation and denial. We have new organizations with bright, capable people working on this," he said. "So it's perplexing to me why the president won't be just straight up about the threat from Putin and Russia."
"I did my best to serve the president and the country," he said, when pressed by Karl about what an adviser is to do when a president makes decisions counter to their personal judgement. "I wasn't going to hold back ... I didn't care. I wasn't trying to keep my job. I wasn't trying to get a next job."
"I concluded, you know, as a historian in particular, that the greatest disservice not only to the country, but also to the president himself, would be if I held back, if I didn't tell him what he didn't want to hear," said McMaster, who has a Ph.D. in American history and currently lectures at Stanford University. "And so that's what I did for 13 months."
The retired lieutenant general used that lens as he contextualized politics' current polarization during the interview and offered potential remedies for the government and the media.
"None of these problems that we're facing are going away while we're at each other's throats," he said. "We should probably be focused on doing our part to bring our society back together and to -- and to try to build a better future for generations of Americans to come."
"We have to restore our pride. We have to restore our confidence. A big part of that is we have to be confident in common sources of authoritative information," he added.
McMaster noted that during his more than three decades in the Army, he never voted, so as "to keep that bold line in place" between the military "and partisan politics." Now that he has retired however, he revealed that the 2020 election marks a personal first.
"I voted for the first time in my life," he said.
But as for whether he cast his ballot for the president, McMaster maintained some military discipline:
"I voted now and will continue to vote and will never tell anyone ever how I voted," he said.