Sen. John Cornyn (R-Tex.), Sen. Lindsey Graham (R-S.C.) and others are standing up for Attorney General Jeff Sessions after President Trump suggested he wants Sessions to resign. (The Washington Post)

For arguably the first time, Republicans are starting to draw red lines in an effort to save President Trump from himself.

As Trump weighs firing one or both of Attorney General Jeff Sessions and special counsel Robert Mueller, a pair of GOP senators is promising measures to thwart or dissuade him. Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa) said Wednesday that his panel would not confirm a new attorney general to replace Sessions this year. Then Thursday morning, Sen. Lindsey O. Graham (R-S.C.) said he would introduce legislation to protect Mueller and warned it “could be the beginning of the end” of Trump's presidency if he tried to fire the special counsel.

Both moves are unprecedented. For perhaps the first time, Senate Republicans with real sway are talking about concrete steps to counteract Trump's impulses and prevent constitutional crises.

Republicans have spent plenty of time talking tough about Trump, mind you. Plenty of them said Trump's comments about women on that “Access Hollywood” tape were beyond the pale, and some even urged him to drop out of the presidential race. Many of these same members, such as Rep. Jason Chaffetz (R-Utah), would later embrace Trump. (Chaffetz has since retired from Congress.)

Like Graham, Sen. John McCain (R-Ariz.) has been among the most vocal Trump critics in the GOP, including giving a brutal speech denouncing Trump's worldview in February in Munich. But even that speech didn't call out Trump by name, and McCain has frustrated Trump's opponents by not backing up his words with actions, such as voting against Trump's agenda.

House Speaker Paul D. Ryan (R-Wis.), too, has been called upon to occasionally denounce Trump. And sometimes he has obliged. But he has also assumed a nonconfrontational approach to dealing with the president, repeatedly brushing off his tweets — including as recently as Thursday morning — in favor of trying to work with Trump to get things done.

There have been some threats of legislation or actions by Republicans to stop Trump. In January, for instance, GOP senators led by McCain threatened a bill to prevent Trump from lifting sanctions against Russia. Similarly, Graham in March suggested he might call for a special committee to look into Trump's baseless allegation that President Barack Obama wiretapped him.

But this is the first time the stakes have been this high. And Grassley and Graham are going on-record with specific actions and threats.

Look, politics is an inherently disingenuous business. Sometimes you say something with a little extra conviction to send a message, or you make threats that you're not 100 percent committed to backing up. Politicians also have to deal with the realities of alienating a president who has significant sway over whether they can pass their agenda. There is no doubt Republicans, after denouncing Trump repeatedly on the campaign trail and seeing him win anyway, have grown gun-shy. This is the moment he's gone too far and I can cut him off, they've thought so many times, only to be proven wrong in short order.

I'm not one of those people who thinks McCain can't denounce Trump one day and vote for his agenda the next. McCain is a conservative Republican, so he tends to support Republican legislation. He wants to replace Obamacare, so he voted to move forward with a debate on doing just that this week, despite his reservations about the process.

But at some point, Republicans who think Trump is truly flirting with a constitutional crisis will need to back up their tough rhetoric with actions. Grassley and Graham seem to be at least edging toward doing that — perhaps recognizing the uniquely fraught options Trump is apparently considering.

We'll see how much follow-through there is. But at some point, the rubber must meet the road, or it just amounts to a bunch of talk.

Update: Sen. Ben Sasse (R-Neb.) is also speaking out now, telling Trump not to plan on a possible recess appointment to replace Sessions. "Forget about it," Sasse said. Sasse didn't appear to threaten specific action, though Republicans as a whole could thwart a recess appointment.