Jeb Bush once again told a group he is thinking of running for president. The reason interest is high in an undeclared candidate with loud (if not numerous) opponents within the GOP is not hard to figure out. With each passing week it becomes more apparent that there is a gap in the GOP field, which Jeb or some other candidate needs to fill in order for the GOP to win the White House. That candidate may be among the group of governors who are considering a run, but we haven’t seen anyone step forward in commanding style to fill that role, which for lack of a better term we will call the center-right grown-up.

Indiana Gov. Mike Pence signs legislation, Monday, March 24, 2014 at the Indiana Career Council Meeting at the Indiana State Library.  (AP Photo/The Indianapolis Star, Rob Goebel)
Indiana Gov. Mike Pence in March. (Rob Goebel/Associated Press via the Indianapolis Star)

Such a candidate must be prepared and interested in national security. If that person is not already fully up to speed on the myriad of international challenges, the potential grownup should be hitting the books, talking to experts and traveling — now. I will be blunt: If the person is too busy now, either because there is a reelection campaign looming or his or her day job takes too much time, it is unlikely the person will be able to get command of the facts, articulate reasoned views and be able to go toe-to-toe with Hillary Clinton. If you wait until the presidential announcement date to learn history and geopolitics it will be too late. If potential candidates think they are busy now, wait until a presidential campaign comes along. Running for president may be the hardest thing they will ever do, and time for gaining national security proficiency will be virtually nonexistent.

As for an interest in foreign affairs, presidents are often confounded by how much attention national security demands of the president. Tending to our nation’s security is often thankless, unpopular and distracting. Unseasoned political operatives can get antsy when the president becomes engaged in foreign policy for days on end, rather than raising money or rolling out a popular domestic program. Unless the candidate is actually interested in and recognizes the centrality of national security to the job, he will be unwilling to devote the time and political capital to the task. Moreover, if you have to start from scratch because your attention to or interest in national security up until now is so scant, you might pass on the presidency. We currently have a president who has tried to wing it — with terrible results.

In addition, the grownup will need an even-keel personality and a highly professional staff that can battle for the candidate effectively without getting into a blood match with every critic. The voters can tell when a presidential candidate is comfortable in his own skin and his staff is up to speed and confident about its candidate. Voters will need to imagine these people dealing with foreign crises or difficult lawmakers. If the candidate and/or the circle of advisers are frantic, bellicose, slipshod or ignorant, voters will run the other way.

The reason, I suspect, Jeb Bush is stirring so much interest is that there are grave doubts, not only among the donor class, about whether there is a grown-up among the potential contenders. Will Indiana Gov. Mike Pence decide to run? Can Texas Gov. Rick Perry show 2012 was a fluke, put his down-time after he leaves office to good use and show he is presidential material? Will Wisconsin Gov. Scott Walker develop a presence that connotes “commander in chief,” or will he be 2016′s Tim Pawlenty? Has New Jersey Gov. Chris Christie settled doubts and risen above Jersey politics? Does Rep. Paul Ryan (R-Wis.) really want to leave the House after making it to the chairmanship of Ways and Means?

So long as these questions swirl and the choice might come down to a freshman senator or a lackluster governor unschooled in foreign policy, the  “Get Jeb!” sentiment will grow. If conservatives for whatever reason don’t like him, then it behooves them to find their own grownup. Otherwise  we can start wondering if we should call Bill Clinton “first mate” or “first gentleman.”

Jennifer Rubin writes the Right Turn blog for The Post, offering reported opinion from a conservative perspective.