Kennedy was nominated by Ronald Reagan in 1987 and has been on the bench for over 3 decades. He is consider to be a conservative but his viewpoint is to the left of Trump’s. He has indicated that he would be retiring for the last few months. He has submitted his resignation to be effective on July 31.
Presently the court is comprised of four liberal leaning judges and four conservative judges. Kennedy was the swing vote on several recent landmark votes by the SCOTUS, like the legalization of same sex marriages, the preservation of Roe v. Wade, the upholding of warrantless wiretapping and the overturning of the handgun ban.
Potential replacements are Brett Kavanaugh, William Pryor, Thomas Hardiman, Amul Thapar, Raymond Kethledge and Amy Coney Barrett. Since the Republicans hold a 51 – 49 edge in the Senate, a Trump nominee could be approved without any bipartisan support. Democrats are not happy.