Justice Anthony Kennedy's announcement today that he is retiring from the US Supreme Court effective July 31 has opened the floodgates of speculation on who US President Donald Trump will choose as his replacement.

Here is a look at the seven judges who are considered front-runners. With the exceptions of Amy Coney Barrett and Amul Thapar, all are George W. Bush appointees.

Brett Kavanaugh
Where: Of Maryland, US Court of Appeals for the District of Columbia Circuit.
Who: A graduate of Yale College and Yale Law School, Kavanaugh was appointed in 2006 by Bush to the US Court of Appeals for the DC Circuit. He previously worked in the Bush White House as Assistant to the President and Staff Secretary and was a partner at the Kirkland & Ellis law firm. Notably, in 1993, Kavanaugh worked as Kennedy's law clerk.

Raymond Gruender
Where: Of Missouri, US Court of Appeals for the 8th Circuit.
Who: Gruender has been on Trump's shortlist since before the 2016 election. A graduate of Washington University in St Louis, he worked as the Missouri state director for GOP nominee Bob Dole's presidential campaign in 1996 and went on to serve as US Attorney for the Eastern District of Missouri before the Senate in 2004 confirmed him to his current job in a 97-to-1 vote.

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Thomas Hardiman
Where: Of Pennsylvania, US Court of Appeals for the 3rd Circuit.
Who: Hardiman was among those interviewed by Trump last year to fill the vacancy left by Antonin Scalia's death. He took an unconventional route to the federal bench: He was the first in his family to graduate from college and drove a taxi to help pay for his education. He is a Georgetown University Law Centre alumnus and is also reportedly the favourite of Trump's sister, Judge Maryanne Trump Barry, with whom he serves on the US Court of Appeals for the 3rd Circuit.

Raymond Kethledge
Where: Of Michigan, US Court of Appeals for the 6th Circuit.
Who: Kethledge is also a former Kennedy clerk and was among those under consideration by Trump last year. The University of Michigan graduate was originally nominated to his current job by Bush in 2006, but due to opposition from Michigan's two Democratic senators, he was not confirmed until a compromise deal was reached two years later. Before joining the bench, he was the legal counsel for former senator and Secretary of Energy Spencer Abraham.

William Pryor
Where: Of Alabama, US Court of Appeals for the 11th Circuit.
Who: Pryor is a veteran of the political fights surrounding judicial picks. In 2003, he was nominated by Bush to the appeals court, but it took a recess appointment and a two-year standoff before Republicans and Democrats finally crafted a deal that confirmed him to the position. Pryor is a conservative and harsh critic of Roe vs Wade, which he has called "the worst abomination of constitutional law in our history." He is a protege of Attorney-General Jeff Sessions.

Amy Coney Barrett
Where: Of Indiana, U.S. Court of Appeals for the 7th Circuit.
Who: Barrett is a relatively new appeals court judge in Chicago, confirmed last year after a bruising confirmation fight. Democrats questioned whether Barrett, then a law professor at the University of Notre Dame, let her Catholic faith play too big a role in her legal thinking. That line of questions angered religious conservatives, who rallied to support her. She insisted her faith would not interfere with her role as a judge, and was confirmed.

Amul Thapar
Where: Of Kentucky, U.S. Court of Appeals for the 6th Circuit.
Who: Thapar has been a federal appeals court judge in Cincinnati for about a year. He worked as a federal prosecutor in Kentucky before eventually becoming a district court judge. Thapar is a favourite of Senate Majority Leader Mitch McConnell, and as a candidate, Trump said he would consider Thapar as a Supreme Court pick.