Senator John McCain, the chairman of the Senate Armed Services Committee, and Senator Ben Sasse sent a joint letter to the Trump administration Thursday urging them to coordinate with NATO allies to respond to Russia’s use of a nerve agent in Salisbury, England.

The bottom line: If NATO countries join the U.K. in expelling Russian diplomats from their countries or choose to freeze Russian assets, they would be sending an undeniably clear message to Russia that its shadow operations will not go unpunished among NATO allies.