In the Trump world, nothing is certain until it happens, but there are rumblings that President Trump isn't yet finished with his staff shakeup. After firing Secretary of State Rex Tillerson by tweet Tuesday, it's possible other administration officials also may be leaving as soon as this week.

The sense that H.R. McMaster's days are numbered as national security adviser has reached something close to a fever pitch. Several sources inside and outside the White House say they expect McMaster to leave this week and, in all likelihood, return to the Army with the anticipation that the three-star general will be given a fourth star. This would be part of the easing out deal Defense Secretary James Mattis (who retired as a four-star general) has quietly nudged along.

Former U.N. Ambassador John Bolton, is waiting in the wings to replace McMaster. That is the expected outcome -- he has been patient and persistent, and he shares Mr. Trump's hostility toward the Iran deal. Secretary of State-designate Mike Pompeo also opposes the Iran deal, unlike Tillerson, who had fought hard to keep the president from ripping up the deal.

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Congressional sources and White House advisers tell CBS News that Housing and Urban Development Secretary Ben Carson is in serious jeopardy. There is an expectation he also will not last the week in the Trump administration. After emails released Wednesday showed that Carson knew more about the expensive furniture ordered for his office than he had previously let on.

Veterans Affairs Secretary David Shulkin is also in danger of losing his job because of continued fallout from his travel expenses and the Inspector General report about misinformation tied to that travel spending. Shulkin had hoped that paying back the travel costs would solve the problem, but it has not. Congressional sources and White House advisers now believe Energy Secretary Rick Perry will move over to the VA to replace Shulkin. One reason Shulkin has not already been removed is the lack of a confirmable replacement. Perry is seen as a "good fit" at VA and sources say he is willing to make the move -- and they believe he could be confirmed.

It's not clear who would replace Carson at HUD or Perry at Energy, should they vacate their positions.