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“Let’s face it, the president of the United States is the only person who can stop Putin from this act of aggression,” said Mr. McCaul, chairman of the House Committee on Homeland Security, though he added that European countries also have a role to play.

But the ongoing battle over the circumstances surrounding the downed jetliner itself and the aftermath represents yet another devolution in U.S.-Russian relations after Russia’s annexation of the Crimean Peninsula, formerly a part of Ukraine, and continued fighting by Russian-backed rebels along eastern Ukraine’s border with Russia.

Asked on CNN whether she believes U.S.-Russian relations are now at Cold War levels, Sen. Dianne Feinstein, California Democrat and chairwoman of the Senate Select Committee on Intelligence, responded simply, “Yes.”

Mrs. Feinstein said the nexus between Russia and the separatist rebels has been established “very clearly.”

“So the issue is where is Putin?” she said. “And I would say, ‘Putin, you have to man up. You should talk to the world. You should say if this was a mistake — which I hope it was — say it.’ Even if it was a mistake, it’s a horrendous mistake to make.”

This article is based in part on wire service reports.