WASHINGTON (Reuters) - President Donald Trump will be advised by a small group of deeply conservative lawyers, some inside the White House and at least one from outside, on choosing a nominee to the U.S. Supreme Court to replace Justice Anthony Kennedy, said several sources familiar with the process. Kennedy announced his retirement on Wednesday.

White House Counsel Don McGahn will be Trump’s lead adviser on the pick, having successfully guided the nomination of Justice Neil Gorsuch through the selection and confirmation process last year, White House sources said.

Leonard Leo, an outside legal activist, will be another key member of the president’s advisory team, sources said.

Leo is on leave from his position as executive vice president of the Federalist Society, an influential conservative legal group that regularly gathers like-minded lawyers and judges at conferences and on law school campuses nationwide. He helped compile a 25-person list of likely nominees from which Trump has said he will make his selection.

Also central to the vetting and interviewing process will be two associate counsels to the president: Rob Luther and David Morrell, said former Justice Department lawyer John Malcolm, now an analyst at the Heritage Foundation, a conservative think tank in Washington.

“They’re smart and tapped into the conservative legal community,” he said. “They’re very skilled at what they do.”

Like-minded advocacy groups are expected to mount efforts to assure the nominee is confirmed, and the Judicial Crisis Network has said it will spend at least a million dollars in the effort.

FILE PHOTO: White House Counsel Don McGahn sits behind U.S. President Donald Trump as the president holds a cabinet meeting at the White House in Washington, U.S. June 21, 2018. REUTERS/Jonathan Ernst

The group’s campaign will urge voters to pressure their senators to ensure confirmation. The group has already produced a new TV advertisement calling Trump’s list of 25 potential candidates the “best of the best” and warning that his opponents will lie and attack the nominee.

Trump met on Thursday with a group of six senators - three Republicans and three Democrats - to discuss the court vacancy, the White House said in a statement.

The Democrats - Joe Manchin of West Virginia, Joe Donnelly of Indiana and Heidi Heitkamp of North Dakota - are running for re-election in November in states Trump won in 2016. Two of the Republicans - Lisa Murkowski and Susan Collins - are abortion-rights supporters and could balk at voting for a Trump nominee who would overturn the 1973 Roe v. Wade landmark abortion decision.

The other senator who met with Trump, Republican Charles Grassley, is chairman of the Judiciary Committee, which will consider any Trump choice.

People familiar with the selection process said the front- runners on Trump’s list at this point are all current federal appeals court judges: Brett Kavanaugh, a judge on the District of Columbia U.S. Court of Appeals; Thomas Hardiman, who serves on the Philadelphia-based 3rd U.S. Circuit Court of Appeals; Raymond Kethledge of the 6th U.S. Circuit Court of Appeals; Amul Thapar, whom Trump named to the 6th Circuit; and Amy Coney Barrett, whom Trump named to the 7th U.S. Circuit Court of Appeals.

All five have spoken at Federalist Society events.

Two sources close to the process said Trump has also expressed interest in Utah Senator Mike Lee, who has the support of Texas Senator Ted Cruz. Both senators are Republicans.

The complication for a Lee nomination is that if he joined the court, a Republican Senate seat would be vacated at a time when Republicans hold only a narrow 51-49 Senate majority.

Trump could be reluctant to take Lee out of the Senate because of past experience. When he tapped Alabama Senator Jeff Sessions to be attorney general, Sessions’ replacement in the Senate ended up being a Democrat, despite Alabama’s traditional conservatism.

Trump “likes Mike, and Mike would do it. But the problem you face is, you have to make sure you have the Senate,” one source said.