MOSCOW — The national security adviser, John R. Bolton, is in Moscow this week to explain to officials President Trump’s decision to pull out of a 1987 arms-control pact.

Mr. Trump and his hard-line aides, particularly Mr. Bolton, have long expressed their displeasure with the agreement, the Intermediate-range Nuclear Forces Treaty, because they say Russia is in violation of the terms and China is not a signatory.

“Unless Russia comes to us and China comes to us and they all come to us and they say, ‘Let’s all of us get smart and let’s none of us develop those weapons,’ ” America would pull out and start building new nuclear arms, Mr. Trump said after a campaign rally on Saturday.

In response, the Kremlin spokesman, Dmitri S. Peskov, hinted at a new arms race, saying Russia would be forced also to develop new weapons “to restore balance in this sphere.”