With Texas temperatures around 100 degrees, voting in a primary runoff election may not be on most Texans' minds, but candidates are hoping a few hot races will bring voters to the polls.

Early voting is underway for the July 31 runoff elections in Texas.

The hottest race in the state seems to be the Republican primary runoff for U.S. Senate between Lt. Gov. David Dewhurst and former state Solicitor General Ted Cruz.

The two were forced into a runoff in the May 29 primary election when no one in the field of seven candidates was able to garner more than 50 percent of the votes. Dewhurst came in first with 45 percent of the votes, but the second place finisher Cruz was more than 10 points behind with 34 percent.

But polls show Cruz has been narrowing the gap since May, and has been raking in contributions from out-of-state donors. The 41-year-old Cuban-American attorney has received support from the Tea Party and more than $4 million from the Club for Growth, a group that is pro-free market.

Cruz has 25 percent of his donations coming from contributors outside of Texas. Dewhurst, on the other hand, is getting financial aid primarily from Texas donors. His out of state donors only make up 5 percent of his funding base.

The battle has come down to Cruz and Dewhurst each claiming to be the true conservative in the race.

Dewhurst, 66, has presided over the Texas Senate as lieutenant governor since 2003. Cruz claims Dewhurst supported a state payroll tax, advocates Medicaid expansion and is soft on immigration.

They both oppose the Affordable Care Act, both say they want to curb spending and cut taxes.

With a mid-summer election, pundits expect a very low voter turnout.

The Cruz camp says it believes his supporters, mainly highly motivated Tea Party members, will get out to the polls no matter what, so his camp is not concerned with low voter turnout. The thinking is that those who do vote will be voting for Cruz.

The Democrats are also having a runoff for the Senate seat being vacated by Republican Kay Bailey Hutchison.

Paul Sadler, a former state representative, is facing Grady Yarbrough, a retired teacher. Yarbrough previously ran for land commissioner as a Republican and for state treasurer as a Democrat.

Since Republicans outnumber Democrats across Texas, the winner of the July 31 Republican runoff will likely win the Senate seat.

The other race heating up the runoff election is for state Senate between incumbent Jeff Wentworth and Donna Campbell.

Before the May 29 primary, Wentworth and Railroad Commissioner Elizabeth Ames Jones, who had the backing of Texans for Lawsuit Reform, were embroiled in a TV ad war and a lawsuit.

But Jones came in third, leaving Campbell, an emergency-room doctor, to face the senator in the runoff. Jones has since endorsed Campbell.

According to the Texas Ethics Commission reports, Wentworth raised $316,888 between May 20 and June 30. He also has $256,123 on hand.

In contrast, Campbell raised $65,791 during the same time period, and has less than half of Wentworth's cash on hand -- $107,597.

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