Romney has 997 of the 1,144 delegates needed after primaries in Arkansas and Kentucky last week, CNN reported. Texas has 155 delegates awarded proportionally by district and statewide.
However, U.S. Rep. Ron Paul, R-Texas, has said he would actively work state party conventions instead of the campaign trail, and has succeeded in picking up delegates and installing supporters as leaders along the way.
The Texas primary typically is in March, but a battle over redistricting pushed it to Tuesday, well after many other states cast ballots in their presidential primaries.
And a possible runoff in July looms if no one in the Republican primary for the U.S. Senate polls a majority. A recent University of Texas/Texas Tribune poll indicated Lt. Gov. David Dewhurst held a single-digit lead over former Solicitor General Ted Cruz, a Tea Party favorite.
The poll indicated former Dallas Mayor Tom Leppert had 17 percent, broadcaster and former football player Craig James had 4 percent and the remaining five GOP candidates brought up the rear in vying to be the candidate tasked with keeping the seat of retiring Sen. Kay Bailey Hutchison in the Republican column, the Fort Worth Star-Telegram reported.
Daron Shaw, a University of Texas-Austin government professor and co-director of the poll, said Cruz positioned himself to the right of Dewhurst for the primary, giving himself a big advantage even though Dewhurst was the leader early last week.
"It's not surprising that David Dewhurst is still in front," poll co-director Jim Henson, a University of Texas-Austin professor, told the Star-Telegram. "We're seeing the advantages we expected him to have from the beginning of the campaign."
The number of contenders has worked against Dewhurst, Henson said, noting Cruz and Leppert "are claiming some real estate."
"If they're in a runoff, Dewhurst is in trouble," Shaw told the newspaper.
Democrats also could be racing to a July 31 finish in the U.S. Senate primary race, most likely between former state Rep. Paul Sadler and Sean Hubbard, with Sadler leading but Hubbard behind and within the margin of error, the poll indicated.
Taking advantage of early voting, Texas Gov. Rick Perry said he cast his ballot for Mitt Romney, the presumptive GOP presidential nominee.
Perry, who dropped out of the race to be the party's nominee against President Obama in January, also predicted his once-bitter campaign rival would win in November, USA Today reported.
"On a scale of [one to] 10, show me as a 10," Perry was quoted as saying in The Texas Tribune about his support for the former Massachusetts governor. "We don't really have an option here if you're a person who cares about the future of this country."
Perry, who endorsed Newt Gingrich immediately after exiting the campaign, now touts Romney's "private sector experience" as something Obama doesn't have.
Perry and 2008 GOP vice presidential candidate and former Alaska Gov. Sarah Palin are telling Texans their candidate is the best one to fill Hutchison's seat. Of course, they're backing different candidates, USA Today said.
Perry backs Dewhurst, calling him in an ad "the one candidate best prepared to make conservative change happen in Washington."
But Palin begs to differ, saying in a robocall that Cruz is a "conservative you can trust to stand by on principle and change the way Washington does business."
Too bad some of her robocalls were routed to Kansas.
The Topeka Capital-Journal reported receiving a robocall in the newsroom that began, "Hello, Texas! I'm Sarah Palin."
The reason for the glitch was not immediately known.
As ads inundate the airwaves, one radio commercial in a Central Texas state Senate race triggered a lawsuit by the candidate it attacks.
Texas state Sen. Jeff Wentworth has called accusations he billed the state and his campaign fund for the same travel expenses is "completely false," KENS-TV, San Antonio, reported.
He filed a defamation suit against his primary opponent, former Texas Railroad Commissioner Elizabeth Ames Jones, who countersued, claiming the accusation is true.
And accusations of lying -- although no lawsuit had been filed yet -- don't stop there.
In the Republican primary for Hutchinson's seat, front-runner Dewhurst and Cruz also traded attack ads, each accusing the other of lying about his opponent.