Late last month, the Obama administration announced its intention to purchase 32 tons of Iranian heavy water for $8.6 million. The justification provided for the purchase is that the Joint Comprehensive Plan of Action (JCPOA) mandates Tehran only hold a certain amount of heavy water in its possession, and Iran has stockpiled more, so the excess has to be sold.

In the days following the announcement, Sen. Tom Cotton, R-Ark., proposed an amendment to a $37.5 billion energy and water-oriented spending bill restricting the US from future purchases of Iranian heavy water. The reaction to Cotton’s proposal was astounding. At first, Senate Democrats derailed the entire spending bill. Eventually, the minority party agreed to allow a vote on Cotton’s amendment, but only if Republicans agreed to require a 60-vote threshold for passage. The amendment failed after receiving 57 votes in support.