O'Rourke, who is challenging Republican Senator Ted Cruz for one of Texas' seats in the U.S. Congress, was speaking to a HBCU town hall in Prairie View, Texas, when he made the stinging comments against the police.
O'Rourke has garnered national attention in the race and has elevated Democratic hopes for defeating Cruz, and neutral observers say the race is competitive. A recent Reuters/Ipsos poll gave O'Rourke a slight edge, with 47 percent to Cruz's 45 percent, but that came on the heels of a Quinnipiac University survey that showed Cruz up by nine percentage points. CBS News rates the race as Lean Republican.
The upscale University Park area surrounding the serene college campus where Friday night's debate will take place is exactly the type of battleground that both Cruz and O'Rourke need to perform well if they want to emerge victorious in November.
The Texas conservative and O'Rourke have agreed to three debates; this is the first of the three. White voters back Cruz 66 - 32 percent.More news: A year after deadly Maria, Puerto Rico still struggles with aftermath
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The candidates will also debate on September 30 at the University of Houston and on October 16 in San Antonio.
Signs of a victory by O'Rourke, a USA congressman from El Paso, in deep-red Texas would likely herald a nationwide Democratic voter wave that could be catastrophic for Republicans. He has complained that outside Democratic groups are providing O'Rourke with a fundraising advantage.
Cruz has criticized O'Rourke as a liberal out of touch with Texan values.