President Trump is fortunate to have U.S. Sen. Lindsey Graham poised to take over the chairmanship of the Senate Judiciary Committee. He will need Sen. Graham at his back if House Democrats freshly armed with subpoena power unleash a series of efforts to bring down his presidency.

If Senate Republicans follow through in January in naming Sen. Graham the next Judiciary chairman, President Trump will certainly get that support. But his scrappiness is not the only reason Mr. Trump needs the South Carolina Republican. The success of major parts of the president’s legislative agenda for the next two years will depend in part on Sen. Graham’s skill in finding bipartisan solutions.

The Judiciary Committee chairmanship will be a challenging test of Sen. Graham’s two main strengths as a legislator — his willingness to confront any argument, even from his own party, that he thinks is wrong, and his ability to reach out to the other side.

Sen. Graham’s rise to the Judiciary Committee chairmanship and his close working relationship with President Trump — a man he has criticized on occasion — give him a chance to put parts of his own agenda to the test and open the door to possible further deals such as the elusive “grand compromise” on a sustainable budget.

In recent interviews Sen. Graham has reviewed his legislative priorities and his willingness to work with Democrats. On Nov. 16 he said, “If I am fortunate enough to be selected by my colleagues to serve as chairman, I will push for the appointment and Senate confirmation of highly qualified conservative judges to the federal bench and aggressive oversight of the Department of Justice and FBI.”

A particular focus, he said, will be on getting a clear picture of how decisions were made when James Comey was FBI director in 2016.

On Sunday’s “Meet the Press” he said prison reform legislation is an opportunity for Republicans and Democrats to work together on a breakthrough issue. “The Republicans are the problem here, not the Democrats,” he said, urging President Trump to get busy making calls to win votes for the legislation, which the White House supports.

He also said that he has promised the ranking Democrat on the Judiciary Committee, Sen. Dianne Feinstein, D-Calif., and other committee Democrats “to try to find a way to do something on immigration. There are a lot of things we could do on that committee in a bipartisan fashion.”

Sen. Graham clashed strongly with Sen. Feinstein during the confirmation hearings for now Supreme Court Justice Brett Kavanaugh, winning conservative support he has sometimes lacked. But he has made a point of finding common ground with Democrats on many issues. If he can find a path to enacting immigration reform and prison reform with White House support, it would clear up two major legislative bottlenecks.

Sen. Graham’s combination of conservative principles and a readiness to compromise on controversial questions has been a regular and commendable feature of his legislative career. It also has sometimes earned him the enmity of more doctrinaire conservatives who object to working with the opposition on issues like prison reform and especially immigration.

If he takes the path he has recently described, he will undoubtedly face opposition in the South Carolina 2020 Republican senatorial primary. But his political risk will be less if he brings President Trump along with him.

The next two years are going be very interesting ones for both of them.