The West’s response to Russian aggression has usually been too little, too late, and devoid of the one voice that really matters — President Trump’s.

But at last, his administration is taking action, and Mr. Trump has spoken out, tentatively. On Thursday the Treasury Department announced it was imposing sanctions for the Kremlin’s interference in the 2016 election. Officials have denounced the poisoning of a former Russian spy in Britain and Russia’s devastating bombing missions in Syria.

While such steps are encouraging, only a more robust, unified response from the United States and its NATO allies would impede President Vladimir Putin from expanding his pattern of heinous behavior.

Before leaving office, President Barack Obama expelled 35 Russian diplomats, seized two diplomatic properties and imposed sanctions in response to the election interference. Mr. Trump, for reasons that have never been made completely clear, has until now resisted a congressional mandate that he expand the penalties. This was despite the warnings of intelligence agencies that Russia is already trying to meddle in the 2018 election and Congress’s near unanimous passage of the law demanding more sanctions.