WASHINGTON — Vice President Mike Pence visits three countries in Russia’s neighborhood beginning Monday to signal support for them and NATO while drawing a line against aggression.

Pence’s trip to Estonia, Georgia and Montenegro is viewed as a follow-up to President Donald Trump’s visit to Europe earlier this month. Then, Trump used stops in Poland and Germany to try to pull off a tricky balancing act of improving ties with Moscow while also presenting the U.S. as a check against Russia’s moves in the region.

Pence’s mission will be encouraging those countries to continue to ally with the West and resist Russia’s attempts to splinter the NATO alliance.

Defense Secretary Jim Mattis and Secretary of State Rex Tillerson have previously been dispatched to try to allay the concerns of countries near Russia that the U.S. really will stand behind NATO and support the sovereignty of non-member former Soviet republics.

The concerns stem from Trump’s suggestion during the campaign that the U.S. might not defend NATO allies and his apparent desire for closer relations with Russia. Trump received criticism on his first European trip for passing up the chance to affirm the NATO mutual defense commitment clause known as Article 5, which frames an attack on one as an attack on all. Trump did affirm U.S. support for Article 5 on his second trip to Europe.

The vice president is expected to deliver a message of support for U.S. trade and investment with the countries while underscoring the U.S. commitment to the security of the three nations, according to senior administration officials who briefed reporters about the trip on the condition that they not be identified by name. Pence also will stress the values of freedom of speech, democracy and religious tolerance.

In Estonia, Pence is expected to highlight bilateral ties with the U.S., particularly on trade, investment and cyber issues. Pence also is expected to thank Estonian officials for their approach to “burden-sharing,” diplomatic speak for agreeing to spend a full share of 2 percent of their GDP on defense, the administration officials said.

The vice president also is expected to underscore the U.S. commitment to NATO, which sees Russia as a security threat and offers protection to concerned member states near Russia’s borders.

In Georgia, Pence is expected to highlight U.S. support for its sovereignty and territorial integrity, the officials said. Georgia is the only country on the trip that is not a NATO member and, like Ukraine, has seen Russian encroachment on its territory. The administration officials said the U.S. is encouraging Georgia to continue to make reforms to its judiciary and expand anti-corruption efforts.

In Montenegro, Pence will celebrate that nation as the newest NATO ally.

On Wednesday, he’ll attend the Adriatic Charter Summit in Podgorica, Montenegro, to highlight the U.S. commitment to the Western Balkans and underscore the importance of good governance, political reforms and rule of law. Also expected to attend are the leaders of Albania, Bosnia and Herzegovina, Croatia, Kosovo, Macedonia, Serbia and Slovenia.