President-elect Donald Trump. (Matt Rourke/Associated Press)

ALTHOUGH PRESIDENT Obama’s sanctions against Russia for interfering with the U.S. presidential election came late, his action on Thursday reflected a bipartisan consensus that penalties must be imposed for Moscow’s audacious hacking and meddling. But one prominent voice in the United States reacted differently. President-elect Donald Trump said “it’s time for our country to move on to bigger and better things.” Earlier in the week, he asserted that the “whole age of computer has made it where nobody knows exactly what is going on.”

No, Mr. Trump, it is not time to move on. U.S. intelligence agencies are in agreement about “what is going on”: a brazen and unprecedented attempt by a hostile power to covertly sway the outcome of a U.S. presidential election through the theft and release of material damaging to Democratic nominee Hillary Clinton. The president-elect’s dismissive response only deepens unanswered questions about his ties to Russia in the past and his plans for cooperation with Vladi­mir Putin.

For his part, Mr. Putin seems to be eagerly anticipating the Trump presidency. On Friday, he promised to withhold retaliatory sanctions, clearly hoping the new Trump administration will nullify Mr. Obama’s acts. Then Mr. Trump cheered on Twitter: “Great move on delay (by V. Putin) — I always knew he was very smart!”

For any American leader, an attempt to subvert U.S. democracy ought to be unforgivable — even if he is the intended beneficiary. Some years ago, then-Defense Secretary Leon Panetta warned of a “cyber-Pearl Harbor,” and the fear at the time was of a cyberattack collapsing electric grids or crashing financial markets. Now we have a real cyber-Pearl Harbor, though not one that was anticipated. Mr. Obama has pledged a thorough investigation and disclosure; the information released on Thursday does not go far enough. Congress should not shrink from establishing a select committee for a full-scale probe.

Mr. Obama also hinted at additional retaliation, possibly unannounced, and we believe it would be justified to deter future mischief. How about shedding a little sunshine on Mr. Putin’s hidden wealth and that of his coterie?

(Bastien Inzaurralde/The Washington Post)

Mr. Trump has been frank about his desire to improve relations with Russia, but he seems blissfully untroubled by the reasons for the deterioration in relations, including Russia’s instigation of an armed uprising in Ukraine, its seizure of Crimea, its efforts to divide Europe and the crushing of democracy and human rights at home.

Why is Mr. Trump so dismissive of Russia’s dangerous behavior? Some say it is his lack of experience in foreign policy, or an oft-stated admiration for strongmen, or naivete about Russian intentions. But darker suspicions persist. Mr. Trump has steadfastly refused to be transparent about his multibillion-dollar business empire. Are there loans or deals with Russian businesses or the state that were concealed during the campaign? Are there hidden communications with Mr. Putin or his representatives? We would be thrilled to see all the doubts dispelled, but Mr. Trump’s odd behavior in the face of a clear threat from Russia, matched by Mr. Putin’s evident enthusiasm for the president-elect, cannot be easily explained.