Former U.S. Rep. Charles Djou says he is leaving the Republican Party.

Djou, in a column written for the online news site Civil Beat today, cited the party’s leadership under President Donald Trump as the main reason that led to his decision.

Djou wrote,“Today after much consideration, I abandon my party because I am unwilling to abandon my principles. I can no longer stand with a Republican Party that is led by a man I firmly believe is taking the party of Lincoln in a direction I fundamentally disagree with, and a party that is unwilling to stand up to him.”

He added he is “most disappointed by the failure of the GOP to clearly and consistently condemn Trump’s childish behavior.”

“Sadly today, too many Republicans either applaud Trump’s tirades or greet them with silent acceptance. This leads to an implicit ratification by the GOP of Trump’s undisciplined, uninformed, and unfocused leadership as a core part of the Republican Party. This is something I cannot accept and will not be a part of,” Djou wrote.

Hawaii Republican Party Chairwoman Shirlene Ostrov told the Honolulu Star-Advertiser that Djou’s departure from the state GOP is disappointing but not entirely unexpected since Djou repeatedly expressed his unhappiness with Trump even before he was elected president.

“We’re actually sincerely disappointed in Charles Djou’s decision to leave the party, especially at a time where our new leadership team … is moving steadily forward with what I think is a bold agenda, and we are poised to make some gains in the 2018 elections, but we respect his right to make such a decision, and thank him for his many years of service,” Ostrov said. “As a Republican, he stood against a one-party system for a long time.”