The top five candidates vying for the U.S. Senate will square off Tuesday night in the first televised debate of the primary campaign, in a race that has yet to fully engage the public.

Only three weeks before the primary election on Nov. 8, all five have a path to making the two-person runoff.

The five who qualified for the 7 p.m. debate are three Republicans – State Treasurer John Kennedy, U.S. Rep. Charles Boustany and U.S. Rep. John Fleming – and two Democrats: Foster Campbell, a member of the Public Service Commission, and Caroline Fayard, an attorney.

Louisiana Public Broadcasting will air the 90-minute event statewide, and stream it on its website, before a live audience at the Howard Center for the Performing Arts at Louisiana Tech in Ruston.

“The debate is important because we have such a crowded and competitive candidate field that the margin between making the runoff and not making the runoff is very, very small,” said Joshua Stockley, a political science professor at the University of Louisiana-Monroe. “This is a critically important opportunity to distinguish themselves. You’ll come in with certain themes and messages you intend to articulate, but you never truly know what’s going to happen and what people will say when the lights come on.”

A second Senate debate will take place on Nov. 2 at Dillard University in New Orleans, sponsored by Raycom Media, which has four stations in Louisiana.

To qualify, candidates will have to receive at least 5 percent in a poll being conducted by Mason-Dixon Polling & Research, said Vicki Zimmerman, Raycom’s regional news director. She expects the polling company to release the results on Friday.

In all, the Senate field includes 24 candidates, but such candidates as retired Air Force colonel Rob Maness and white supremacist David Duke – both Republican – did not make the cut Tuesday night.

The five candidates who will appear have been prepping for the debate in recent days. Campbell, for example, prepared while at his farm near Elm Grove, which is south of Bossier City.

“We’re making a pitch to undecided voters who want to see someone who will operate with common sense principles,” said Mary-Patricia Wray, the campaign’s spokeswoman.

Campbell is airing a television commercial that features an on-camera endorsement by Gov. John Bel Edwards, his most prominent supporter.

Campbell, 69, a former state senator, has held elected office longer than Fayard, 38, has been alive, a point in her core message.

“Louisiana is ready for a new generation of leadership and a new kind of leader,” said her spokesman, Beau Tidwell.

Fayard’s most prominent supporters are Mary Landrieu, who served 18 years in the Senate, and Mitch Landrieu, New Orleans’ mayor.

Fayard, who lives in New Orleans, lost the 2010 race for lieutenant governor, her only bid for elected office.

Fayard has said she will vote for Hillary Clinton, the Democratic presidential nominee, while Campbell has been reluctant to say who he will support.

Campbell has said that humans are responsible for climate change while Fayard has been reluctant to ascribe blame.

Most polls in the race have showed Kennedy with the lead, but other surveys have shown that he has dropped and is running neck-and-neck with other candidates.

All three Republican candidates have said they will vote for Donald Trump, the party’s presidential nominee, but Fleming and Kennedy have not been shy about endorsing the businessman and his populist message while Boustany has offered only tepid support.

Asked to describe his message Tuesday night, Kennedy said, “I would like to demonstrate that I understand the issues and will stand up for Louisiana values.”

Kennedy, an attorney who switched to the Republican Party in 2007, has the most campaign experience of any candidate in the race, having won five elections for treasurer and lost two for the Senate. He ran the 2004 race for Senate when he was still a Democrat in a year in which he endorsed the Democratic presidential candidate, then-Sen. John Kerry of Massachusetts.

Kennedy’s Democratic past is likely to be one of Fleming’s talking points.

“You’re going to see a message that he’s the one true and trusted conservative in this race,” said Matthew Beynon, Fleming’s spokesman. “This is an opportunity for voters to see differences among the candidates. Dr. Fleming is very eager to make that contrast.”

Fleming, a family practice physician, represents northwest Louisiana and lives in Minden, which is about 40 miles west of Ruston.

Boustany, a heart surgeon from Lafayette, represents southwest Louisiana and most of the coastal parishes.

To appear in Tuesday night’s debate, candidates had to poll at least 5 percent and to have raised $1 million.

The debate moderators will be Beth Courtney, the chief executive officer of Louisiana Public Broadcasting, and Barry Erwin, a former television news reporter who is president and chief executive officer of the Council for a Better Louisiana, a pro-business advocacy group in Baton Rouge.

The four reporters asking questions are: Kelly Spires from LPB; Elizabeth Crisp from The Advocate; Jeremy Alford from LaPolitics.com; and Greg Hilburn from Gannett Newspapers.

Follow Tyler Bridges on Twitter, @tegbridges.