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Beto O'Rourke doesn't buy the criticism of Beyonce -- that she waited too long to throw her support behind him in the Texas Senatorial election -- to the contrary, he says it's hard to find anything from Houston more impressive than her.

We got Beto on Capitol Hill, and he can't say enough about Bey ... can't say enough because he's interrupted by a slew of fans who went nuts when they saw him.

As for Beyonce, some of Beto's supporters think it was too little, too late throwing her support behind him on the day of the election.

Gotta say ... he's about as genuine as they come -- unspotted by the ever-present phoniness of politics.