The 81-year-old justice, who has served on the U.S. Supreme Court for 30 years, was known as a swing vote on some issues.
Cornyn also noted that in 2010, another midterm year, Democrats controlled the Senate and were perfectly happy to confirm an Obama nominee, Elena Kagan, to the high court. Although conservative, he sometimes joined the liberal wing of the court and authored landmark opinions on cases dealing with abortion, campaign finance and LGBT rights, including same-sex marriage.
His retirement sets the stage for a major showdown in the Republican-led US Senate over the confirmation of Mr Trump's eventual pick for the lifetime appointment to replace Justice Kennedy, all coming before November elections in which Democrats are seeking to seize control of Congress from Mr Trump's Republicans.
Abortion is likely to be one of the flash points in the nomination fight.
US Supreme Court upholds Trump's travel ban
He issued his first version just a week after taking office, though it was quickly halted by the courts. Again, people were split on whether the travel ban will make the United States more or less safe.
Human body found in beer cooler at Atlanta Braves' SunTrust Park
The investigation is ongoing as the medical examiner tries to determine how the man died. The department announced later Tuesday that it had been found in a beer cooler.
In shocker, longtime Congressman Joseph Crowley loses Democratic primary in NY
We should also keep in mind there is a pendulum in American politics that Trump has not destroyed. If Ocasio-Cortez wins in November, she will become the youngest woman ever elected to Congress.
Republicans now hold a bare 51-49 majority in the Senate, although that includes the ailing Sen. But to many folks, one thing was certain: lit is dead. Majority Leader Mitch McConnell invoked the nuclear option, lowering the threshold from the super majority of 60 votes that is normally required for confirmation to a simple majority.
"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. The conservative justices on the court give loads of leeway to a president (in this case, a insane one who has been compromised by a foreign power) to dictate immigration policy.
Kennedy's vote, positioned at the very centre of the court, gives him a place of special prominence among the nine justices.