The tweet said Turkey should be ready for a political realm without Bahceli, who has had health issues in recent weeks, which lead to speculation regarding the seriousness of his condition.
The dispute comes at a time when relations between the NATO allies are strained due to Turkey's threats of an incursion into northeastern Syria, after Ankara accused Washington of stalling efforts to establish a 'safe zone' there together.
Bahceli is the leader of Nationalist Movement Party (MHP), which is an ally of President Tayyip Erdogan's AK Party. The two parties entered the parliamentary and presidential elections in an alliance last year, which allowed them to attain a majority in parliament together.
Turkey's Foreign Ministry said on Sunday it had summoned the U.S. Charge d'Affaires to the ministry and requested an "open and clear" explanation regarding the issue.
The AK Party said on Twitter that the user who had posted the message was wanted for links to the network of Fethullah Gulen, which Ankara says orchestrated the abortive coup in July 2016.
Omer Celik, spokesman for the AK Party, said the U.S. State Department and Embassy needed to investigate the issue and an apology would not suffice.
"It shows that some people employed in the Embassy are making a special effort to damage the relations between the two countries," Celik said on Twitter.
"The United States Embassy needs to try to understand Turkey not through people linked with terrorist organizations but through people who can conduct proper analysis," he said.
The Embassy posted an apology on Twitter late on Saturday.
"Earlier today our Embassy Twitter account "liked" an unrelated post in error. We regret the mistake and apologize for any confusion," it said. The like was also removed from the Embassy's page.
Semih Yalcin, deputy head of the MHP, said on Twitter late on Saturday that Bahceli has recovered from his illness and would return to work in the coming week.The relations between the NATO allies have been under pressure in recent years over a range of issues, including Turkey's purchase of Russian S-400 missile defense systems, differences in policy in Syria and the detention of local U.S. consulate employees and citizens in Turkey.