As Ukraine waits in the looming shadow of a potential Russian invasion, the question on everyone’s mind — most of all Vladimir Putin’s — is just how far President Biden is willing to go to enforce the rules of international order and protect our democratic friends. The president’s latest moves have been encouraging: He has positioned more U.S. troops into NATO countries and prepared heavy sanctions on Kremlin officials and their families should Russia invade.

The problem is that these moves have come much too late, suggesting that the president’s heart is not in them. Instead of leading with strength, he has played up to Moscow’s escalations, allowing Putin to drive each successive stage of the crisis. Perhaps most damaging is that he has telegraphed his determination never to send U.S. troops or provide air support to Ukraine. Strong presidents never take options off the table, and we cannot be surprised if Putin now doubts whether we really care what he does to Ukraine.

This could have dangerous consequences for U.S. interests around the globe. If America’s will to lead and defend the free world is no longer believed, every U.S. adversary will be emboldened to challenge our interests.

There are now several dominoes lined up that stand to fall behind Ukraine.

Should Putin invade, Poland and our Baltic allies could be next in line to face Russian hostility. Even now, Moscow has positioned forces in Belarus and the Russian city of Pskov, fewer than 50 miles from Latvia and Estonia. Beyond Europe, North Korea is again ramping up ballistic-missile tests, and Iran is aiming at a final sprint toward a nuclear weapon, raising the specter of a Middle East arms race. To the east, China continues to eye an invasion of Taiwan, which many U.S. officials predict is likely by 2027. The shock waves of such an event would be felt globally. In the U.S., we could expect a stock-market plunge, more supply-chain delays, and a chronic chip shortage, further driving up the cost of autos and electronics.

In each of these trouble spots, President Biden’s handling of Ukraine will either chasten or embolden our adversaries, setting the tone for global power for years to come.

The president’s recent movement of U.S. troops to Poland, Romania, and Germany was a welcome show of strength after months of weakness. With Russian troops once again amassing on Ukraine’s border, President Biden should redouble his efforts by imposing sanctions as punishment for the chaos Russia has already caused. Senate Republicans have introduced bold legislation to achieve this, but not many Democrats have thus far joined our initiative.

Preventing war in the immediate term, however, will not be enough. Putin and his newfound friends in Beijing will continue to test our defense posture for weaknesses. Confronting them will require a concerted effort to regain military superiority.

On this front, the president has not inspired confidence. While China now boasts the world’s largest navy, President Biden’s slim defense proposals would allow our Navy fleet to fall even farther behind. Russia and China are also leaping ahead in missile technology, developing hypersonic weapons that are years ahead of U.S. capabilities. As we learned during the Cold War, we cannot afford to lose the power of deterrence. The results could be catastrophic.

Thankfully, there is a historical template for the kind of course correction we need. The Reagan defense buildup that helped win the Cold War and avoid armed conflict in fact began under President Jimmy Carter in 1980, who pivoted in response to global events. This time around, defense dollars will once again be crucial. But President Biden also needs to rally the American people to the cause. Our citizens deserve to know why these global threats matter and impinge on our very way of life.

President Biden can right the ship on his handling of this crisis, but he needs to recognize the global stakes at hand. Putin wants to use Ukraine to destroy faith in America’s willingness to lead the free world. President Biden must not allow that to happen.

Read the op-ed in National Review here.