Last week, the United States signed a five-year extension of the New START arms control treaty with Russia. Russia’s President Putin signed the treaty shortly thereafter. The “Strategic Arms Reduction Treaty” allows Russia and the US to monitor each other’s nuclear forces, facilities, and activities. The idea is to keep track of the relative strength of the two regimes' respective arsenals and to encourage reductions. The treaty also caps the number of deployed strategic nuclear warheads at 1,550 each. (The total stockpiles for the US and Russia are 4,700 and 4,300, respectively.) The move is a departure from the Trump administration’s opposition to the treaty. The Trump administration had wanted to renegotiate the treaty, insisting that so-called tactical nuclear weapons—designed for battlefield use—be included. As it is, the treaty focuses only on strategic weapons. The Trump administration also insisted that China be added to the treaty. The Chinese declined to participate. President Trump also ended two other arms treaties, the Intermediate-Range Nuclear Forces (INF) Treaty and the Open Skies Treaty.