Police secure the street outside the Turkish Embassy in Washington during a visit by Turkish President Recep Tayyip Erdogan on May 16. (Dave Clark/Agence France-Presse via Getty Images)

IN THE four months since the violent attack on peaceful protesters by Turkish bodyguards during President Recep Tayyip Erdogan's visit to Washington, nothing has made the Turkish government own up to this outrageous assault on democratic principles on American soil. Not protests from the State Department, not bipartisan condemnations from Congress and not the indictments of Turkish security officials on criminal charges. Perhaps a threat to block certain weapon sales will be a more meaningful way to suggest there is a price to be paid for such brutality.

Turkey's continued intransigence about the events of May 16, in which 11 people were injured in a melee outside the Turkish ambassador's residence, prompted a Senate committee to approve a measure that would block the U.S. government from supporting the sale of weapons to security forces protecting Mr. Erdogan. "We are not going to let President Erdogan's personal bodyguards attack peaceful American protesters on American soil — and we're certainly not going to sell them weapons while they do it," said Sen. Chris Van Hollen (D-Md.), who co-sponsored the amendment with Sen. Patrick J. Leahy (D-Vt.) that was approved this month on a bipartisan vote in the Senate Appropriations Committee.

Video of the demonstration showed protesters being chased down, kicked and beaten by men who included members of Mr. Erdogan's security detail while the Turkish president looked on complacently. Nineteen people, including 15 identified as Turkish security officials, were indicted on felony charges, but most are believed to have left the United States and only two have been taken into custody. The Justice Department won't comment on whether it is seeking extradition, and the Turkish government has been uncooperative to the point of insult. That Mr. Erdogan called the indictments "a clear and scandalous expression of how justice works in America" is in keeping with the utter contempt he has displayed so brutally in his own country toward the right to dissent, a free press and an independent judiciary.

This amendment, part of a larger spending bill for the State Department that now goes to the full Senate, makes clear, said Mr. Van Hollen, “that we don’t want U.S. taxpayer dollars to be used for . . . cracking down on dissenters in Turkey and the United States.” Congress should approve the measure, and the president should sign it.