(CNN) – A boiling primary battle in Texas may come to an end Tuesday as voters cast their ballots for the Republican pick in the state's open U.S. Senate seat.
While Lt. Gov. David Dewhurst leads the crowded field of candidates, the real test will be whether he can cross the 50% threshold required to secure the nomination and avoid a July 31 runoff contest.
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His biggest threat so far is tea party favorite Ted Cruz, a former solicitor general with strong support from national groups and high profile conservative leaders.
Polls show Dewhurst in the lead, but Cruz has gradually been catching up, pushing ahead of other contenders including former Dallas Mayor Tom Leppert and ESPN Broadcaster Craig James.
This race is particularly important as the balance of power in the U.S. Senate could shift in 2012. It is also another test in the staying power and influence of tea party groups and their political strategy to focus more on congressional races than on the presidential campaign.
The race, held to replace retiring Sen. Kay Bailey Hutchison, has seen a Texas-sized level of spending, as well. According to Federal Election Commission reports, more than $31.6 million has been dumped in the GOP primary as of May 9, with more than half coming from Dewhurst's team.
While Cruz's campaign has spent more than $4 million, the underdog has been boosted by a surge of outside spending. The fiscal conservative organization Club for Growth has dropped more than $2 million, and the tea party oriented FreedomWorks has also been heavy on the ground in get-out-the-vote efforts on behalf of Cruz.
Members of the Tea Party Express, a leading arm of the grassroots movement, have traversed the state by bus in support of Cruz. Adding to his rising star power, the form solicitor general landed endorsements from former GOP presidential candidate Rick Santorum and tea party stalwart Sarah Palin, two big voices in the conservative movement.
Dewhurst, meanwhile, touts his support from 2008 presidential candidate and former Arkansas Gov. Mike Huckabee.
Texas Gov. Rick Perry, who's worked alongside Dewhurst for nearly 10 years, has also been vocal for his No. 2. In a recent commercial, Perry urged voters to turn out for Dewhurst, insisting he was the true conservative in the race.
Given that Perry and Dewhurst have worked together for almost a decade, some political observers characterize the race as a possible referendum on Perry, the state's longest-serving governor in history.
But Perry brushed off the idea on Friday, telling CNN Chief National Correspondent John King that while national conservatives may be making noise in the race against Dewhurst, the local movement will stand for the lieutenant governor.
"There's, you know, people who come from out of state and make their endorsements known," Perry said. "But Texas conservatives are lining up behind David Dewhurst."
And while Cruz largely poses the biggest challenge for Dewhurst on Tuesday, one of the lieutenant governor's latest ads targeted Leppert, the former Dallas mayor, a move that suggests Dewhurst may be angling to add enough Leppert supporters to his column in the final days before the primary to cross the 50% mark.
Dewhurst opponents criticize the candidate as being part of the Republican establishment and having too many years in government under his belt. Before becoming lieutenant governor, Dewhurst served as Texas Land Commissioner in the late 90s.
Hitting back, Dewhurst points to his private sector experience as the co-founder of Falcon Seaboard, an energy company based in Houston. He also boasts his role in pushing for socially conservative legislation in the state, including a recent bill that requires women to see a sonogram and go through a 24-hour waiting period prior to having an abortion.
For his part, Dewhurst has attacked Cruz, who is of Cuban descent, as a supporter of amnesty and a member of the Hispanic Leadership Fund and the Hispanic Alliance for Prosperity Institute. Cruz has also been on the defense over criticism that he works for a firm representing a Chinese company being sued for patent violations.
The candidate has repeatedly shot down both claims, arguing he has long been an opponent of illegal immigration and saying he is not the lead lawyer in the patent lawsuit.
The Hispanic Leadership Fund also fired back against Dewhurst's latest ad, saying Cruz has never had any position with the group and faulted the ad as dishonest.
"The Hispanic Leadership Fund support using free market and limited government principles to strengthen border security, restore a functional legal immigration system, and promote patriotic assimilation. If David Dewhurst wants to deceitfully lump us in with leftist organizations that actually do promote amnesty, then all he is accomplishing is demonstrating to Texas voters how intellectually shallow he is," Mario Lopez, the organization's president, said in a statement.
On the Democratic side, former state Rep. Paul Sadler and political operative Sean Hubbard are competing for their party's nomination.
Texas has not elected a Democrat to the Senate in more than two decades.
Political handicappers Stuart Rothenberg and Charlie Cook, however, both rate the open seat as safe for Republicans.