When U.S. Sen. David Vitter used the opening forum of the 2015 gubernatorial campaign season to tout his leadership on a bipartisan congressional highway bill and vow to press ahead on a follow-up, one of his rivals seized on the opening.

“This is precisely why we want to you stay,” Lt. Gov. Jay Dardenne quipped, eliciting laughter from a ballroom full of engineers, contractors and others who do business with government.

It was a good line, rivaled only by Vitter’s smiling comeback: “I’ll take the compliment but not the suggestion.”

It’s also a real issue, one of several raised by the four announced candidates at last Friday’s opening face-off, sponsored by American Council of Engineering Companies of Louisiana and several related groups, that likely will re-emerge on the campaign trail throughout the year.

No doubt Vitter had a good 2014. In the contest for the state’s other Senate seat, he got the result he not only wanted but helped engineer, three-term Democrat Mary Landrieu’s defeat at the hands of Bill Cassidy. He got the Republican takeover he wanted, too, complete with a committee chairmanship on small business, a scenario that leaves him with as much power as he’s had in Congress to date.

But his success also gives his rivals, not just Dardenne but Public Service Commissioner Scott Angelle, who playfully seconded Dardenne’s motion, and state Rep. John Bel Edwards, some ammunition. It’s worth considering whether Louisiana would be better off with at least one senior senator rather than two beginners, and expect these three to keep making the case.

The exchange came as Vitter was arguing his own point, one that he too will surely bring up again.

Vitter often plays the conservative ideologue, but contrary to popular belief, he insisted that he can cross the aisle. As ranking Republican on the Environment and Public Works Committee, he said he’s worked with the committee’s Democratic former chairwoman, California’s Barbara Boxer, on the highway measure and on bills governing water resources — even though he and Boxer weren’t just on opposite ends of the political spectrum, they were the opposite ends of the spectrum.

That fits in with something Vitter’s already hinted he’ll do in the campaign, try to moderate his hard-line image — a goal that’s particularly important for him as he faces the possibility of a runoff with Dardenne or Angelle, both fellow Republicans.

Edwards, the only Democrat in the field, sought to establish himself as the one true change from Gov. Bobby Jindal. This is more of a challenge than it might first appear, because, despite their common party affiliation, both Vitter and Dardenne are openly running against Jindal’s record.

Edwards argued that he’s fought Jindal’s policies more strenuously than anyone else on the stage. At another point in the forum, he mentioned his opposition to a divisive bill that Jindal championed, legislation to cut off the levee authority lawsuit against oil and gas companies for damage to the coast. If the state immunizes the industry, he asked, how can it ask outsiders for help?

Meanwhile, Angelle, a former Democrat and the one candidate with no legislative voting record, highlighted both his conservative upbringing and his executive experience working on issues such as creation of the state coastal restoration plan. He mostly skipped the part about how much of that experience came while working for Kathleen Blanco and Jindal.

And there was one more point that came through loud and clear from all four contestants. Each was able to talk in detail about funding roadwork and coastal restoration, reforming the rainy day fund, and revising a capital outlay process that Angelle said he found bewildering in his early days as a St. Martin Parish official and still considers “confusing by design.” In short, each showed off an impressive mastery of the complexities of state government.

They may not stress that when they’re out there talking to the public. After all, it’s more fashionable these days to be an outsider than a career politician.

That would be too bad, because so many of the problems facing the state are structural and demand an insider’s knowledge. And if there was one takeaway from the forum, it’s that the strength of this particular gubernatorial field is in its collective on-the-job training.

Stephanie Grace can be contacted at sgrace@theadvocate.com. Read her blog at http://blogs.theadvocate.com/gracenotes. Follow her on Twitter, @stephgracenola.