(CNN) Bob Corker is no Donald Trump hater. Which makes what the Tennessee Republican senator said Thursday about the President all the more powerful.

"The President has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful," Corker told reporters following a speech in Chattanooga

Later, he sounded a similar note: "We should hope that (Trump) aspires that he does some self-reflection, that he does what is necessary to demonstrate stability, to demonstrate competence, to demonstrate that he understands the character of our nation and works daily to bring out the best of the people in our nation."

Stability. Competence. Stability. Competence.

Words matter in politics. Corker, who was the mayor of Chattanooga before being elected to the Senate in 2006, knows that. Which is why his repeated emphasis on Trump's "stability" and "competence" matter.

Corker is clearly hinting at the possibility that Trump is not simply misguided in some of his policies and pronouncements -- but that he may be fundamentally unfit for the office that he currently holds.

Doubt it? Ask yourself what the opposite of stable and competent is. It's unstable and incompetent. Corker doesn't go all the way there but he is absolutely leading people to ask those questions by choosing the words he did.

In doing so, Corker is raising the stakes in the conversation Republicans are currently having about what to do about Trump in the wake of his controversial comments about the motivations of the protesters in Charlottesville over the weekend.

Condemnation is one thing. We wish Trump hadn't done this, it doesn't represent us and we hope he doesn't do it again.

Questioning competency is something else -- and something far more serious. It takes the question away from what Trump said to why he said it. As in, is he even aware that what he is saying is a total abdication of moral (and political) leadership? And, if not, what, if anything, can be done about it?

That such a question comes from Corker makes it something that Republicans -- inside the Congress and outside it -- won't likely ignore. Corker, unlike some of his Senate colleagues like Lindsey Graham, John McCain and Ben Sasse, avoided bashing Trump during the campaign and kept an open line of communication with the party's nominee.

As a result, Corker was part of Trump's veepstakes ( he ultimately removed himself from consideration ) and was mentioned as a possible Secretary of State once Trump won.

Corker has kept up those relationships. As CNN's Jeremy Herb noted : "Corker has maintained a collegial relationship with Trump and his administration, and he has spoken regularly with both the President and Secretary of State Rex Tillerson."

This is not someone who hates Trump taking a cheap shot. This is a respected lawmaker who bears no ill will toward President Trump bluntly raising questions about whether the occupant of the Oval Office is up to that job.

That's serious stuff. And Republicans would do well to treat it that way.

CORRECTION: This story has been updated to add a dropped phrase back into Corker's quote.