Leahy, the Senate Judiciary Committee chairman, introduced a same-sex marriage amendment to the immigration reform bill that would give equal protection to immigrants who are in same-sex marriages. His amendment would allow the partner of a U.S. citizen to apply for a green card the same way heterosexual married couples are able to do.

Leahy planned to offer his amendment during the committee markup process, but he withdrew it after Republicans and the Democratic members of the Gang of Eight threatened to vote against it. On Wednesday, he called that “one of the most disappointing moments” of his Senate career.

Sen. Marco RubioMarco Antonio RubioAdministration works to assuage critics over ZTE deal Hillicon Valley: Judge rules Trump can't block Twitter users | ISIS content finds a home on Google Plus | Rubio rips ZTE demands as 'terrible deal' | Bill would protect kids' data Overnight Finance: Trump eyes 'different structure' for China trade deal | Trump mulls auto import tariffs | Banks get green light to offer short-term loans MORE (R-Fla.), a leading conservative in the Gang of Eight, threatened he would no longer support the bill if Leahy’s amendment succeeded.

Leahy said he “took Republicans at their word” that they would no longer support the bill if his amendment were part of it.

On Wednesday morning, the Supreme Court struck down federal discrimination within the Defense of Marriage Act in a 5-4 decision. Leahy applauded the decision but said he would continue to work on gay-rights issues.

“Today’s decision should be seen as a victory for all those who support justice, equality, and family values," Leahy said. "There is still important work to be done so that all families are protected under our federal laws. Until we fully achieve the motto engraved in Vermont marble above the Supreme Court building that declares 'Equal justice under the law,' I will continue to fight for the equal treatment of all Americans."