Such unrestricted drug importation is currently prohibited by law.

The policy has widespread support among Americans: one Kaiser poll taken in 2015 found that 72 percent of Americans are in favor of allowing for importation. President-elect Donald Trump also campaigned on a promise to allow for importation.

The Senate voted down the amendment 52-46, with two senators not voting. Unusually, the vote was not purely along party lines: 13 Republicans joined Sanders and a majority of Democrats in supporting the amendment, while 13 Democrats and a majority of Republicans opposed it.

One of those Democrats was New Jersey's Cory Booker, who is considered a rising star in the party and a possible 2020 presidential contender.