After a procedural vote earlier in the week, the accession treaty for the small Balkan nation to join the transatlantic alliance yesterday sailed through on a 97-2 vote.
The measure now goes to the White House for Trump's formal ratification.
To date, 25 other NATO members have ratified Montenegro's accession, a country of 620,000 people seen as a geostrategic ally. The Netherlands and Spain have yet to do so.
The North Atlantic Treaty Organization holds its summit on May 25 in Brussels, where Trump will use the opportunity to reaffirm Washington's strong commitment to the alliance, according to the White House.
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The Kremlin is opposed to Montenegro's accession, calling it a "provocation" that would reinforce the pro-Western military alliance's presence in the Balkans.
The US vote comes days after a Montenegrin special prosecutor accused "Russian state bodies" of involvement in an alleged coup plot during Montenegro's October election.
Russia also stands accused of interfering in the US presidential election last year, when US intelligence agencies say it leaked hacked emails that damaged Democrat Hillary Clinton's campaign.
Several senators have framed Montenegro's accession as nothing less than a test of resolve against Russian President Vladimir Putin.
Republican Senator Susan Collins said she was "very happy that the Russian campaign to try to dissuade the people of Montenegro from joining NATO, and the disinformation that Russia disseminated, was not successful."
Ben Cardin, the top Democrat on the Senate Foreign Relations Committee, said Montenegro's membership sends "a strong message of resolve to Russia as it invades its neighbors and seeks to upend the international order."
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