Here are the ominous signs for Trump that his support among key Republicans may finally be falling apart

The past few weeks have been brutal for President Donald Trump, with Russia revelations continuing apace and federal investigators closing in on his associates as they implicate him in illegal payoff schemes.

Until now, Trump has been able to rely on the steadfast support of Senate Republicans, nearly all of whom vote for his agenda over 90 percent of the time and many of whom actively dismiss the significance of Trump being involved in crimes.

But lately, cracks have started to appear in their resolve.

Last week, Sen. Marco Rubio (R-FL) warned on ABC's "This Week" that Trump should not pardon his campaign chair Paul Manafort, who is likely to spend the rest of his life in prison for bank fraud and tax evasion related to his work for foreign autocrats and oligarchs. "I believe it'd be a terrible mistake," said Rubio. "Pardons should be used judiciously. They're used for cases with extraordinary circumstances."

Even senators who have been some of Trump's most shameless defenders are now showing signs of doubt, like Sen. Orrin Hatch (R-UT). Earlier this week, in shameless disregard for the rule of law, Hatch flatly told a reporter that "I don't care" if Trump committed criminal acts because "since he's become president this economy has charged ahead ... and I think we ought to judge him on that basis." But on Friday, Hatch took back his remark, saying it was "irresponsible and a poor reflection on my lengthy record of dedication to the rule of law" and saying that special counsel Robert Mueller "must be allowed to complete his investigation."

Meanwhile, this week, Senate Republicans have taken votes in the past few days that would seem to rebuke the president's coddling of Saudi Arabia. By a vote of 56 to 41, the Senate passed a resolution calling for an end to U.S. support of the Saudi war in Yemen, which has caused a massive famine from which at least 85,000 children have died. The Senate also passed, by voice vote, another resolution holding Saudi crown prince Mohammed bin Salman responsible for the brutal murder and dismemberment of Washington Post journalist Jamal Khashoggi, just days after Trump confirmed that he still stands by Saudi Arabia and by the prince.

With a slightly larger GOP majority coming into the Senate next year, it is unlikely that the chamber will, in the main, do much to resist Trump. However, several GOP senators are signaling that there are limits to what they will have Trump's back on — and the president should take notice.