India's announcement of a $500 million purchase of Russian warships on Tuesday again illustrates why the U.S. must build stronger relations with the South Asian nation. Absent our close attention to India's interests and concerns, New Delhi will gravitate closer to Russian President Vladimir Putin.

The scale of Putin's success in cultivating India is certainly impressive. This most recent purchase follows India's $5.4 billion agreement last month to buy the S-400 air defense system. India and Russia have also jointly developed a supersonic cruise missile with launch platform flexibility. All of this activity ignores U.S. sanctions that are expressly designed to prevent Chinese and Russian arms exports.

Yet it reflects that India sees Russia as a more valuable arms partner than the U.S. It's true that Russia's offer of cheaper-than-U.S. exports is attractive to India, but Russia also brings outsize benefit in programs like the S-400, for example, which is the world's finest air defense system. And while Trump administration is correcting the Obama administration's error and enabling India quicker access to more and better U.S. military technologies, and to membership of the nuclear suppliers group, it will take time and new U.S. capabilities to effectively wean India off the Russian export market. In the short term, that means America must tolerate Indian dealings with the Russians that we would not otherwise accept. But over time we must make it so that America is India's manifestly preferred partner. We have a natural democratic baseline on which to build that relationship, but doing so will require our attention to every Indian concern.

In the end, this isn't about Russia. It's about availing ourselves of a partnership to maintain the American-led liberal international order in the 21st century. That means building a superpower alignment that constrains the economic, political, and military imperialism of Xi Jinping's China.