Opposition to Russia has been a core value of American policy for decades. Under the Soviet Union and now as the Russian Federation, it has threatened world peace as it pursues its quest for domination. The U.S. favors a system governed by agreed rules; Russia favors chaos.

Russia’s aggression against Ukraine is the latest example of its attempt to gain domination through force. But the surprising ability of Ukraine to resist Vladimir Putin’s version of Russian expansion has given the U.S. and its NATO allies the chance to win their long struggle with a fading world power.

President Joe Biden has led a successful response to Russian aggression without the loss of a single American life on the battlefield. NATO was formed to block Russian expansion in Europe, and it has had to revive its mission as Russia’s attempt to take over its neighbor threatens other nearby nations, including Poland and the Baltic countries.

Ukraine stood up to Russian aggression on behalf of what was often called “the Free World” and the U.S. and its NATO allies backed its willingness to put Ukrainian lives at risk with some of the alliance’s latest weapons.

NATO has grown stronger as its member countries have been shaken from their mistaken belief that Russia, on which they had become dependent for oil and natural gas, would be a good citizen of Europe. Finland, which shares a long border with Russia, and Sweden have moved off the sidelines to seek NATO membership. The alliance has moved its forces closer to Russia.

The NATO countries also imposed possibly the toughest economic sanctions ever levied short of outright blockade. Americans paid the price at the pump, but the cost to Russia will be higher and longer lasting. Putin’s folly may have transformed the world economy for good.

Biden has had bipartisan support in Congress for his Ukraine policies of sending arms, training troops and easing the hardships of war. Traditional GOP opposition to Russia coupled with Biden’s ability to lead a united Democratic contingent have been paying off in successful resistance to Russia, now revealed as a paper tiger, though still one with nuclear weapons.

But some Republicans oppose Biden’s policy. Their numbers may be growing as the war wears on. With GOP control of the House next year, they could try to undercut what has been a successful policy. Ukraine aid is becoming an increasingly partisan issue.

There may be three reasons for the growing Republican opposition. First, they don’t want Biden to succeed. Second, they would revive traditional American isolationism based on ignoring much of what takes place in the world and focusing on our own concerns. Third, some like Putin, because they see him as an efficient authoritarian.

Ukraine President Volodymyr Zelensky and his people may be fighting an unwinnable war, because Ukraine is restrained by NATO from launching a counterattack into Russia. And the weak Russian military is propped up by Iran and must fight to hold its ground but no longer advances.

Each side seeks the best possible positions before the negotiations that will inevitably end the fighting. Russia wants to demoralize Ukrainians by attacks on homes, hospitals and energy facilities, so they will be ready to cede territory. Ukraine wants to recover as much territory as possible before talks begin and relies on continued U.S. arms supplies.

The minute the war halts, it will be fair to say that Ukraine has won and Russia has lost. Russia, which could not take over Ukraine and turn it into a buffer against NATO, has not only failed to annex its neighbor but has seen NATO strengthened. Ukraine has shown it can field a strong army.

The first step toward a negotiated settlement is a cease fire. Ukraine must force Putin to conclude that he must stop fighting and start talking. Zelensky needs strong NATO backing, which depends on the U.S. It’s an illusion to believe that Europe can go it alone without American leadership. Wishing for that won’t make it happen.

The risk is that partisan congressional opposition could reduce or eliminate critical American support and hand Russia an unearned victory instead of ending its great power myth. If the U.S. maintains its support for Ukraine, the result will reduce or eliminate its Russian rival. And it could send a message to China, possibly discouraging an invasion of Taiwan.

The American president is responsible for foreign policy, but Congress has the power of the purse. A bipartisan agreement on foreign policy is a worthy goal. Such an accord does not mean that other goals cannot also be pursued.

Ukraine policy should not come down to opposing a Democratic president, who must never get GOP support, with a Republican “America First” view. Ukraine is both too important and winnable.

Gordon L. Weil formerly wrote for the Washington Post and other newspapers, served on the U.S. Senate and EU staffs, headed Maine state agencies and was a Harpswell selectman.