(CNN) Members of Congress have continued to strongly advise, in public and private, this week that President Donald Trump shouldn't fire Attorney General Jeff Sessions especially ahead of the midterm elections because of the political fallout he -- and the party -- could face.

Trump has been very public about his frustration with Sessions and has been venting to Republican members of the Senate and House for months now, according to several Senate Republican sources with direct knowledge of the conversations.

The President regularly goes on tangents about how Sessions is not serving him well -- specifically Sessions' decision to recuse himself from the Russia investigation. The probe has formed a cloud over the White House, and the President believes it is bogging down his time in office.

But Trump also believes Sessions -- billed as an immigration hardliner -- hasn't done enough to help the President execute on his hardline campaign promises. And he's upset that Sessions hasn't done more to investigate members of the previous administration or the so-called "deep state" that Trump believes are hampering his presidency.

Trump is also dismissive of Sessions' personality, temperament and diminutive stature.

According to Politico , aides have said Trump complains that Sessions "talks like he has marbles in his mouth."

Trump has broached firing Sessions at multiple points over the last year and a half, including as recently as the last several weeks. This has come in multiple venues in addition to discussions with lawmakers, including heated meetings with aides and discussions with outside advisers and friends. One place it did not arise: with Sessions himself. Trump did not raise the matter when they met last week on sentencing reform.

Trump has preferred airing his complaints publicly on Twitter or privately through emissaries, who he will ask to deliver harshly worded messages to Sessions. Trump and Sessions rarely, if ever, speak on the phone, two sources familiar with their relationship tell CNN.

Defending Sessions -- for now

On Tuesday, Sessions received strong words of support from Majority Leader Mitch McConnell. The top Republican senator cannot prevent Trump from firing Sessions, but speaks for the conference.

"I have total confidence in the attorney general. I think he ought to stay exactly where he is," McConnell told reporters.

At this point, Senate GOP aides believe Trump will listen to McConnell and leave Sessions be for the time being. Meanwhile, there is growing recognition that just about everyone expects it's a foregone conclusion that Sessions will be removed shortly after the midterms.

Each time Trump raises the prospect of firing Sessions, lawmakers, aides and advisers have staved off his impulse, arguing to the President that such a move could damage him politically and present further problems with special counsel Robert Mueller. Trump has responded by insisting has the "absolute right" to fire Sessions if he pleases, those familiar with the conversations said.

But he's taken his team's advice until now because he believes his attempts to discredit Mueller are working and accepts the argument that dismissing his attorney general could cloud that effort. Despite his repeated public criticism, Trump has told people he is wary of crossing a line with Mueller by firing Sessions.

The façade of unity the Republicans once had backing Sessions is slowly cracking in part because of concrete policy difference between Sessions and key members on Capitol Hill including Senate Judiciary Chairman Chuck Grassley, an Iowa Republican who has spent years working on a criminal justice reform package that Sessions has signaled he has issues with. Republicans know Trump has soured on him, but it's the policy disputes that are the driving force behind senators cooling on their defense of their former colleague.

"Sen. Grassley has made clear that former Sen. Sessions has a different job then he did in the Senate and he should let the Senate make the policy, make the law and his job is to enforce it," said John Cornyn, R-Texas, the No. 2 Senate Republican. "But I don't think any of those are personal or threaten his tenure."

What's changed

Republican senators on the receiving end of Trump's venting have long just sat and listened or even told him to leave their former Senate colleague alone. They have publicly shown a unified front in support of Sessions.

But in the last two weeks, several have started to open the door to Sessions' removal after the election. While Sen. Lindsey Graham has been the most vocal about that prospect, more telling has been the rank-and-file Republicans who aren't rushing to defend Sessions.

A common refrain -- even when members are defending Sessions -- has become that it is ultimately in Trump's power to decide what should happen to Sessions.

Why this is happening

The reason for the shift is two-fold: Sessions has infuriated several top Republicans with his policy positions of late. Criminal justice reform may seem minor in the grand scheme of things happening in Washington right now, but it's is not, at all, to senators like Graham and Grassley. They've worked for years on it and Sessions has undercut their (and Jared Kushner's) efforts. Add in disputes over immigration or marijuana policy or a handful of other key issues, and you have a real problem with GOP senators who take these issues very seriously.

Think smaller bore policy issues are a strange reason to turn on a Cabinet official? Just remember that it wasn't the mountains of scandal allegations that led the first GOP senators to turn on the Environmental Protection Agency's Scott Pruitt. It was his ethanol policy.

The second reason -- which describes ambivalence more than outright support for a Sessions removal -- is simply resignation that's it's coming. Senators and their aides fully expect Sessions will be fired or forced to resign shortly after the midterm elections.

Where leadership stands

McConnell was unequivocal in his weekly news conference when he said Sessions should stay in his role -- and he had an audience of one, aides say: Trump.

It has also been communicated repeatedly from Hill Republicans to the senior White House staff that Sessions should be left alone until after the election. The political fallout would be immense, especially just months before the midterms where Republicans are laboring to keep their House and Senate majorities.

The procedural fallout would also be a disaster, with Democrats potentially all but shutting down the chamber, and even fellow Republicans saying they won't help confirm a new attorney general.