U.S. Sen. Bob Corker, R-Tenn., speaks in Columbia, Tenn., in August.

U.S. Sen. Bob Corker, a former Chattanooga mayor and two-term Republican senator from Tennessee, said Tuesday he will not seek a third term come the 2018 elections.

"After much thought, consideration and family discussion over the past year, Elizabeth and I have decided that I will leave the United States Senate when my term expires at the end of 2018," Corker, 65, said in a statement. "I also believe the most important public service I have to offer our country could well occur over the next 15 months, and I want to be able to do that as thoughtfully and independently as I did the first 10 years and nine months of my Senate career."

That means our ever-ambitious Corker must have higher aspirations.

Why else would he have felt so free to tell his hometown Rotary Club in August that Trump has not "demonstrated the stability" or "competence" to be a successful president. Corker also said the nation will be "in peril" unless there are "radical changes" at the White House.

some text
Staff file photo by Tim Barber U.S. Sen. Bob Corker, R-Tenn., speaks to the Rotary Club of Chattanooga in August.

It was quite a statement for the chairman of the Senate Foreign Relations Committee and one who rarely criticizes fellow Congress members of either party — let alone the Republican president of the United States.

In September, he doubled down when a Capitol Hill reporter asked if he still stood by those comments. Corker fixed the reporter with steely eyes and said, "You know, I don't make comments without thinking about them."

Perhaps Corker will primary Trump in three years. Or perhaps, if Trump doesn't complete his four-year term, Corker will primary Mike Pence, now vice president.

We could do much, much worse. We already have.

Liberal cable show pundits posited that Corker — a no-nonsense centrist — is leaving because "the Senate is such a mess."

A couple of conservative pundits suggested he knew, with the Iran-deal yoke around his neck, he faced stiff competition from the far right.

But Vanderbilt University political professor John Geer was likely correct when he told The Tennessean: "It scrambles lots of different things because people knew that if Sen. Corker had run for re-election, he might face an opponent in the primary, but he would most likely be renominated and in all likelihood re-elected."

There also has been talk of Corker running for governor, as Tennessee Gov. Bill Haslam is term-limited.

But the gubernatorial election is in 2018 — a tight turnaround for a sitting senator, even one as task-oriented and driven as Corker.

One thing is certain. Corker's decision not to seek re-election leaves a wide-open senate primary. So far there are two main contenders: former Americans for Prosperity-Tennessee Executive Director Andy Ogles, a Republican, and Democrat James Mackler, an Iraqi war veteran and Nashville attorney.

Perhaps Haslam might run for Senate? Could he get more votes than Peyton Manning, who has been rumored to be thinking of a political run in coming years?

We have some interesting elections ahead.