PRESIDENT TRUMP laid out the welcome mat this week for Turkish President Recep Tayyip Erdogan, and the strongman apparently felt so much at home he thought it okay for his thugs to beat up peaceful demonstrators. That Mr. Erdogan has unfortunately been successful in stifling dissent in Turkey doesn’t give him license to come to this country and attack one of its most basic, and cherished, freedoms. It must be made clear that this behavior is unacceptable and will not be tolerated.

A violent confrontation Tuesday evening outside the Turkish ambassador’s residence in Northwest Washington resulted in 11 people being injured. Two people were arrested and charged with misdemeanor assault, and D.C. police said Wednesday the investigation is continuing, with the possibility of other people being charged. Particular scrutiny needs to be paid to the actions of Mr. Erdogan’s security guards, who, a state-owned Turkish news service confirmed, were involved in the fighting because — can you believe the gall? — they didn’t think police were doing enough to quiet the protest.

Video and photographs of the incident show men in dark suits and ties, some holding Turkish flags, kicking and hitting protesters. Uniformed D.C. police officers at various points can be heard telling the men to back off and move across the street. According to D.C. Police Chief Peter Newsham, the situation was especially “dicey” because some of the Turkish guards were armed. “What we saw yesterday — a violent attack on a peaceful demonstration — is an affront to D.C. values and our rights as Americans,” said D.C. Mayor Muriel E. Bowser (D).

This is not the first time Mr. Erdogan has come to the United States and ended up bullying those who dare to disagree with his cruel regime. His appearance at the Brookings Institution during the 2016 Nuclear Security Summit was marred when his security detail roughed up demonstrators and tried to eject “undesired” journalists.

There need to be consequences. The State Department issued a relatively strong statement Wednesday saying that it was “concerned by the violent incidents” involving Turkish security personnel and that the United States is “communicating our concern with the Turkish government in the strongest possible terms.” That’s a good first step, but it is not enough. Turkish personnel instigating this violence must be identified and, if possible, prosecuted or, if shielded by diplomatic immunity, made persons not welcome in this country.