His biggest vulnerability is his diplomatic loneliness. He has nothing close to the web of alliances and partnerships that have anchored the United States and its partners. While it’s almost always slower, harder and less satisfying to work in coalitions, the policy effects are almost always more long-lasting and effective. It’s critical to work with our allies and the Organization for the Prohibition of Chemical Weapons to establish a clear baseline to forcefully counter Mr. Putin’s unserious denials of culpability.

We have demonstrated our ability to work in concert on painful sanctions after Mr. Putin’s invasion of Ukraine. Now it’s time to tighten those screws further, fully apply the sanctions passed by Congress last summer, and work closely with our partners to follow suit. We all need to reduce our vulnerabilities to Russia’s meddling, and deny impunity to those aiding and abetting those efforts.

The project of making Russia great is part and parcel of making Mr. Putin and his crony capitalist friends rich. That is also a vulnerability. Too many countries for too long have facilitated the enrichment and corruption of Mr. Putin’s inner circle. That needs to end.

The logical next step after the diplomatic expulsions is a similarly coordinated campaign to hit the wallets of the Kremlin elite. That won’t be easy or pain-free for a number of economies, including our own. A strong signal that business as usual is over will unsettle Moscow and stimulate concerns about what more drastic steps might follow. Mr. Putin knows that the longer he is denied foreign direct investment, the further behind his economy will fall.

There is some risk of a more forceful response to Mr. Putin’s aggression. We need to be vigilant not to prompt an unprovoked escalation in Ukraine or legitimate Mr. Putin’s shrouded machinations by deploying our own impulsively — whether in cyberspace or other types of covert action. Sustaining military and diplomatic channels is not a favor or a sign of weakness. It’s a way to demonstrate that while we will not give in to Mr. Putin, we will not give up on the longer-term prospect of a healthier relationship with Russia.

It may very well be that last week’s countermeasures are nothing more than a passing phase. We already see cracks within the European Union and Britain is divided by the Brexit debates. The Trump administration has signaled policy shifts, like pulling out of the Iranian nuclear agreement, that will make it easier for Mr. Putin to create wedges.

American actions this past week offer a hopeful sign. Agile diplomacy can still land a punch. Now comes the hard part. Diplomacy won’t transform the adversarial relationship with Mr. Putin’s Russia, but it can manage it. Mr. Putin is right about one thing: We have the stronger cards. We’ve just played them erratically.

Now we should lead with diplomacy and demonstrate its enduring power and purpose. If we don’t, we’ll perpetuate illusions about partnerships with Mr. Putin and the irrelevance of diplomacy — and waste our bigger, better hand.