Picking up where Kissinger left off, Carter also worked for a new strategic arms limitation treaty (SALT II) with the Soviet Union but did not enjoy even a narrow victory. Knowledgeable about nuclear weapons because of his naval service, he feared the destructive power already in existence and hoped to halt the spread of such weapons to other nations and to check the arms race. He pressed the Soviets to agree to cuts in the nuclear arsenals, but Soviet leaders rejected his first proposal. Carter pressed forward, aided by Vance and special arms negotiator Paul Warnke. Negotiations did not break down, and signs of progress emerged from time to time. Yet, foes of a new treaty, such as Senator Henry Jackson, fearful that it would weaken American security, posed the possibility that no treaty acceptable to the Soviets would be ratified by the Senate. The negotiators did not finish work until 1979, and then Republican and Democratic foes in the Senate argued that the Soviets had triumphed in the negotiations, brushing aside the administration's contention that the agreed-upon limits on strategic forces would make the world a less dangerous place and insisting that the United States must increase military spending substantially. The Soviet invasion of Afghanistan weakened prospects still more, persuading Carter in January 1980 to call upon the senators to postpone debate. He continued to favor eventual ratification of SALT II but no longer pressed for it.