Mr. McCain also referred to the consensus among American intelligence agencies that Russia tried to interfere in the presidential election, a contention that Mr. Trump has rejected.

“There’s no doubt that the Russians were hacking,” Mr. McCain said, though he added that he saw “no evidence” that “Russian cyberattacks and leaking of information had any tangible effect on the outcome.”

Toomas Hendrik Ilves, who ended a 10-year term as Estonia’s president in October, said in an interview that the Senate delegation was “more than a business-as-usual visit.”

But Mr. Ilves also played down the idea that the Baltic countries were anxious. “Estonians are not nervous — at best, apprehensive in the face of ambiguous messages,” he said. “Recall that Donald Trump also backed off on his initial statement and, after all, he was talking about those who do not pay enough for defense. We do.”

Mr. Trump said during the presidential campaign that NATO members must pay their share if they want the benefits of a collective defense. Estonia is one of the few NATO members that meet or exceed the benchmark of spending on its military, at least 2 percent of gross domestic spending. (The others are the United States, Britain, Poland and Greece.)

Audronius Azubalis, a Lithuanian lawmaker and former minister of foreign affairs, said in a telephone interview that the senators’ visit “sends a strong message to the Baltic states and those under direct threat — Georgia and Ukraine — that the allies will stand with us” and that the United States would not bow to Russian aggression.

Lithuanians have been alarmed by Mr. Trump’s comments in support of President Vladimir V. Putin of Russia, Mr. Azubalis said, but are now waiting to see if his attitude toward Mr. Putin shifts once he takes office.