AUSTIN, Texas (AP) Former presidential candidate Rick Santorum endorsed Ted Cruz in Texas' crowded race for a U.S. Senate seat on Thursday, saying the firebrand attorney and tea party favorite "has the wow factor."

Cruz, the former state solicitor general, is thought to be trailing front-runner Lt. Gov. David Dewhurst in the Republican primary to replace retiring Sen. Kay Bailey Hutchison. Also vying for the party's nomination are ex-Dallas Mayor Tom Leppert and Craig James, a former running back for Southern Methodist University and the New England Patriots and an announcer on ESPN. If no candidate wins a majority in Tuesday's primary, a runoff will be held July 31.

Santorum, a former U.S. senator from Pennsylvania, first made the announcement on conservative Glenn Beck's radio show and then appeared on a Houston news radio station to explain his choice.

"What we really need, and what we don't have, are people who strongly can communicate and passionately deliver the message on a variety of different fronts, not just on taxes and spending but on the culture and on national security," Santorum told KTRH's Michael Berry.

"We need someone who has the wow factor, who can go out there in front of the media, go out there on the floor of the U.S. Senate, and deliver a strong and passionate message," Santorum said.

He added, "people think it's not important, it is hugely important. It drives the media, it drives the debate in Washington D.C., and it's vitally important that we have someone with Ted's ability and his convictions and that position."

Santorum's presidential bid had enjoyed strong support in Texas but he abandoned it before the state's primary, which was originally set for Super Tuesday but delayed due to a legal battle over redistricting maps drawn by the Republican-dominated state Legislature.

Asked if he would campaign with Cruz, Santorum said "we're working on that" but noted that, if not, he'd be "on the phone and doing whatever I can to influence the election from outside the state."

Cruz has won the support of major national tea party groups including the Washington-based, anti-tax Club for Growth, which says Dewhurst has been too moderate during his nearly nine years as lieutenant governor and has pledged to spend $2 million to defeat him. Former Alaska Gov. Sarah Palin also has recorded a phone message on Cruz's behalf.

Dewhurst said of national interests trying to influence the race in Texas, "It's a campaign ploy. I just laugh it off. Cruz, this is someone who is desperately trying to make things up to be relevant.

"Apparently, some of these groups want their own United States senator that is beholden to them," Dewhurst said in an interview with The Associated Press in Austin. "Quite frankly, I'm not beholden to any special interest. I'm only beholden to the people of Texas who I work for."

Dewhurst has been endorsed by his own pair of failed Republican presidential candidates, Texas Gov. Rick Perry and former Arkansas Gov. Mike Huckabee both featured in television ads praising Cruz's conservative principles.

Dewhurst dismissed Cruz as a simple staffer for the Texas Attorney General's Office, saying "there's a big difference between having the luxury of sitting as a staffer and either writing opinions or offering briefs, and having to stand on the ground when, proverbially, gunfire is going on around you, and make decisions on a real-time basis to move this state forward."