Houston City Councilwoman Amanda Edwards is now the fourth Democrat to jump in the race. A fifth, State Sen. Royce West, is expected to declare next week.

Republican Sen. John Cornyn is facing a growing field of challengers to keep his seat, with the entry of Houston City Councilwoman Amanda Edwards. Other Democratic candidates already in the contest include Air Force veteran M.J. Hegar, former Congressman Chris Bell and Houston activist Sema Hernandez.

Cal Jillson with Southern Methodist University says the crowded presidential contest to challenge President Donald Trump is largely driving the interest in the Senate race.

"I think that represents the uncertainty of the electoral climate as we move toward 2020," Jillson said. "Will President Trump's appeal to racial divisions in the country affect the presidential election and all the Senate elections and House elections going on around the country?"

Jillson says at this stage the large number of challengers to Cornyn could generate enthusiasm among the Democratic base in Texas. Brandon Rottinghaus of the University of Houston agrees.

"A growing primary field for Democrats is a good problem of their own making," Rottinghaus told the Texas Standard. "Twenty-eighteen showed that Texas is winnable, it's flippable, or purple, or it's a toss-up, depending on how you want to characterize it."

Jillson argues that, at this point, the odds still favor Cornyn winning a fourth term, both because of his advantage in cash-on-hand and his greater name recognition.

"M.J. Hegar is out front. Chris Bell won one U.S. House race, lost the governor's race, lost a race in Houston for local office. Amanda Edwards is a local candidate in Houston who has no name recognition outside the city," Jillson said.

A fifth Democrat, State Senator Royce West of Dallas, is expected to declare his candidacy on Monday.

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