(CNN) - Lt. Gov. David Dewhurst took in more money than his Republican opponent in the latest fund-raising period of the bitter Texas GOP Senate runoff.
Dewhurst's campaign said Monday it brought in $5.98 million between May 10 and June 30, with $4.47 million of the amount being lent from his own pocket. Meanwhile his rival, tea party favorite Ted Cruz, announced raising $1.7 million.
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The two Republicans have been dueling it out in an ugly race following the state's May 29 primary. Dewhurst failed at the time to win the 50% needed for the Republican nomination, resulting in a runoff between Dewhurst and Cruz scheduled for July 31.
The race has evolved into one of the most expensive congressional contests of the 2012 election cycle. Through early May, Dewhurst spent more than $17 million to Cruz' $4.3 million, according to the most recent Federal Election Commission records available.
While Cruz lags behind Dewhurst in fund-raising, the tea party favorite has ample support from national conservative groups, including super PACs for FreedomWorks and Club for Growth, the latter of which has spent $1.5 million in the runoff alone.
In an election year with strong anti-Washington sentiment, Dewhurst has made Cruz' ties with the nation's capital a major attack line in the race, especially in his campaign's latest negative ad.
"(Cruz) is a lawyer trained in Washington. Half the money supporting Cruz comes from Washington," the ad's narrator says.
The 30-second spot concludes with the narrator saying: "Lawyer Ted Cruz in Corrupt Washington? He'd fit right in."
Meanwhile, Cruz has also been playing offense, hitting Dewhurst as an establishment Republican with too many years in government. Cruz, who once served as the state's solicitor general (a position to which he was appointed), makes the case on the campaign trail that this is his first time running for office.
Cruz also accuses Dewhurst of supporting a payroll tax, claims which the lieutenant governor strongly denied in the candidates' debate last month.
However, the nonpartisan fact-checking group, Politifact, rated Dewhurst's defense as "false."
"During the state's mid-decade tax debates, the Senate under Dewhurst's leadership - and to his praise - incorporated payroll taxes in a proposal to replace the existing business franchise tax," Politifact's report state. "No payroll tax passed into law. Still, it's incorrect to say Dewhurst never supported a payroll tax."
The two candidates, who are competing to fill the seat soon to be vacated by retiring Sen. Kay Bailey Hutchison, will face off in their next debate on Tuesday.
– CNN's Gregory Wallace contributed to this report.