Opponents of marriage equality on Wednesday lauded Justice Anthony Kennedy's retirement, predicting it would lead to the overturning of Obergefell, in which the Supreme Court found that gay and lesbian couples have a constitutional right to marry.

In a letter to President Donald Trump, Kennedy, 81, informed the president that July 31 would be his last day on the high court.

“For a member of the legal profession it is the highest of honors to serve on this Court,” Kennedy wrote.

While Kennedy was nominated to the court by President Ronald Reagan, he has been the swing vote on many controversial decisions. Kennedy authored majority opinions in four key cases on LGBT rights, including Obergefell and Lawrence, which struck down state sodomy laws in the United States.

“Justice Kennedy literally transformed the lives of lesbian, gay and bisexual people in America,” James Esseks, director of the American Civil Liberties Union's LGBT and HIV Project, told The Washington Post. “He transformed us from criminals in the eyes of the law to having the freedom to marry the people we love most in the world. There are few civil rights journeys as sweeping or as fast, and Justice Kennedy was a key part of that.”

Trump has said that he will pick a conservative justice to replace Kennedy.

The news pushed marriage equality foes into overdrive, who predicted that without Kennedy the court would reverse itself on Obergefell.

“It will give us a legitimate opportunity to remove the lie of same-sex ‘marriage’ that was illegitimately imposed on the nation,” NOM President Brian Brown said in a fundraising email to supporters. “A constitutionalist like [Neil] Gorsuch replacing Kennedy also will greatly strengthen legal recognition of a vast array of religious liberty rights, not to mention the pro-life cause, and the fight for recognition of the truth of gender.”

Mat Staver, founder and chairman of the Liberty Counsel, called Kennedy's retirement a “turning point” for America.

“If Justice Kennedy is replaced with a person who is faithful to the original text and meaning of the Constitution, then it is just a matter of time before several horrible decisions are reversed, including abortion and same-sex marriage,” Staver said in a statement.

Chad Griffin, president of the Human Rights Campaign (HRC), the nation's largest LGBT rights advocate, warned that Kennedy's retirement should “serve as a wakeup call for every pro-equality voter in America.”

“Trump wants a Supreme Court nominee who will undermine progress we've made on affordable health care, LGBTQ equality, Roe and more. The American people don't – and they should have an opportunity to say so at the ballot box in November. The 2018 midterm elections just became the most consequential election of our lifetime. We must keep organizing, mobilizing, and holding lawmakers to account every single day – and then we need to turn out like never before this November,” Griffin said in a statement.