Justice Anthony Kennedy announced on Wednesday that he is retiring, giving President Trump a critical opportunity to move the Supreme Court more solidly to the right in what promises to be an epic confirmation fight.

The 81-year-old senior associate justice informed the White House in a letter of his intention to step down from the high court after 30 years, effective July 31. Justice Kennedy announcement comes a year after  Kennedy’s former law clerk Justice Neil Gorsuch, took over the seat occupied by the late Justice Antonin Scalia.

Arguably the most powerful member of the Supreme Court, Kennedy’s moderate-conservative views often left him the “swing” or deciding vote in hot-button cases ranging from abortion to gay rights to political campaign spending.

President Trump will replace Supreme Court Justice Kennedy with one of 25 people from a previously released list, the White House said after news broke that Kennedy is retiring.  President Trump said the process of nominating a justice will “begin immediately.”  “Hopefully, we will pick someone who is just as outstanding,” Trump told reporters in the Oval Office.  “It will be somebody from this list.”

A Supreme Court vacancy will likely become a key issue in a midterm congressional election year, when control of the Senate is at stake.

The Senate will consider Trump’s latest high court nominee, requiring only a simple majority for confirmation. GOP leaders changed the rules when Gorsuch was being considered, to get rid of the 60-vote procedural filibuster threshold.

But Democrats are expected to try and transform the court opening into a broader political referendum on Trump’s leadership, and the future of social issues like immigration, gun rights, and race.