U.S. Rep. Justin Amash, a frequent critic of President Donald Trump, on Saturday became the first Republican lawmaker to say the president has engaged in impeachable behavior.

Special counsel Robert Mueller's report on the investigation into Russian interference in the 2016 election reveals that Trump "engaged in specific actions and a pattern of behavior that meet the threshold for impeachment," Amash, who has signaled he would consider running as a libertarian against Trump in the 2020 election, wrote on Twitter.

Mueller's report "identifies multiple examples of conduct satisfying all the elements of obstruction of justice, and undoubtedly any person who is not the president of the United States would be indicted based on such evidence," Amash wrote.