Kennedy's departure from that influential role means a second Trump appointment - expected to be more consistently conservative than Kennedy - would shift the Supreme Court further to the political right and solidify that conservative tilt for years.
His retirement, which takes effect on 31 July, gives Mr Trump a second Supreme Court appointment in his 17 months in office after he selected Neil Gorsuch previous year, who has already become one of the most conservative justices. While he voted with the bench's conservatives on campaign finance and, earlier this week, to uphold Trump's travel ban, Kennedy also sided with the Court's liberal justices on issues such as abortion rights, climate change and authoring the majority opinion to legalize same-sex marriage in 2015.
Justice Kennedy's retirement gives Republicans the opportunity to fulfill their promise to install a majority on the court that would overturn these decisions.
Collins said she has the "utmost respect" for Kennedy's service and integrity during his time on the nation's highest court and labeled him "an ideal justice".
"I expect the nominee to be like Justice Gorsuch, to demonstrate excellence in every respect, and to earn widespread support from the American people, and bipartisan support for confirmation in the Senate", Leo said.
Contrary to Matthews' fiery advice, Democrats in the minority have little power to block the nominations of the Republican president, unlike the Republicans who were in the majority when Obama was in power.
"This fall, we will vote to confirm Justice Kennedy's successor". Should Republicans proceed with confirmation hearings before the November election?
The other two older justices, Ruth Bader Ginsburg, 85, and Stephen Breyer, 79, are Democratic appointees who would not appear to be going anywhere during a Trump administration if they can help it.