What will Lindsey do?

It’s the question of the day in Washington: How would Sen. Lindsey Graham, the South Carolina Republican, respond if the probe of President Donald Trump’s relations with Russia reaches a crisis stage?

Graham’s voice would be influential in the Senate if convincing evidence surfaces that impeachable crimes had been committed. The same would be true if Trump tries to derail the inquiry, either by firing the chief investigator, special counsel Robert Mueller, or by replacing Attorney General Jeff Sessions with a loyalist to oversee it.

Graham is a popular figure in the Senate. With his mentor, Sen. John McCain, ailing and absent, Graham could provide a moral and political example.

One of the most interesting debates now raging about the president’s stewardship is the one between Lindsey Graham and Lindsey Graham. The three-term Republican has been both a Trump critic and a Trump sycophant.

He assailed news organizations for depicting Trump as a “kook,” forgetting that’s the word he used to insult candidate Trump in 2016. He has publicly cautioned Trump that firing Mueller “probably” would be an impeachable offense and has called for tougher measures against Russian President Vladimir Putin.

Yet that hasn’t stopped him from acting as a Trump enabler in employing diversionary tactics intended to discredit important aspects of Mueller’s probe and to suppress evidence of a Trump-Russia connection.

Contradictions are nothing new for the 62-year-old former Air Force colonel. As a member of the House of Representatives in 1998, he went along with the Republican leadership and became a manager of the foolish effort to impeach President Bill Clinton for lying about sex with a White House intern. He then broke with the party establishment to support McCain’s 2000 presidential campaign.

A politician of unsurpassed personal charm, he even won over his Democratic opponent, Alex Sanders, after his first Senate run in 2002. Sanders said in defeat that if he’d known that “Lindsey would be that good a senator, I’d have voted for him.”

Even so, watching Graham deal with Trump is like following an instruction manual on how to have it both ways. Like other conservatives, he supported the White House in both its successful tax-cutting initiative and its failed effort to repeal Obamacare, even offering up a slipshod alternative to the Affordable Care Act.

But he also bucked the Republican right wing as a champion of immigration reform. He worked diligently to cut a deal with the White House that could get through Congress; it failed, but immigration advocates applauded his dedication and sincerity.

He explained later that his lavish praise of the egocentric, insecure president was needed to facilitate the immigration deal. That’s plausible for Graham, though it’s also true that he has reason to be wary of inviting a primary challenge from his right flank in 2020.

A longtime foreign-policy hawk, he endorsed the appointment of fellow hardliner John Bolton to become national security adviser. To do so he had to ignore how ill-suited Bolton is for the post, which is meant to supply the president with a variety of foreign policy opinions and options. A model is George H.W. Bush’s adviser, Gen. Brent Scowcroft, who was honest, measured and respected. Bolton, an ideological bully, is the anti-Scowcroft.

There also have been moments when Graham stood out for his candor about Trump. After a private White House meeting in January at which Trump referred to Haiti and African nations as “s---hole countries,” other Republican senators provided shifting defenses of the president’s insults. Graham didn’t. He has also objected publicly to other racial provocations by Trump.

On the Russia probe, the picture is mixed. Graham consistently has defended Mueller and warned Trump that firing the special counsel “could be the beginning of the end of his presidency.”

Yet he joined with Senate Judiciary Committee Chairman Charles Grassley, a conspiracy buff, to demand a criminal investigation of Christopher Steele, a former Russia specialist for British intelligence who assembled a dossier of incompletely vetted reports on Trump’s ties to Moscow. Steele compiled the dossier at the behest of Republican and Democratic Trump opponents; but its contents were deemed credible by McCain, who took it to the Federal Bureau of Investigation.

If the Trump-Russia scandal reaches a critical stage, McCain is unlikely to be available to challenge timid Republicans. Few others could assume that role.

One who might would be his protégé from South Carolina.