Paxton ran unopposed in the May 29 primary.
No he didn't! And the primary was on March 4 not May 29. The runoff was on May 27, and by definition there is an opponent in a runoff election.
Office of the Secretary of State
Race Summary Report
2014 Republican Party Primary Election
3/4/2014
Attorney General
Dan Branch REP 428,325 33.46%
Ken Paxton REP 569,034 44.45%
Barry Smitherman REP 282,701 22.08%
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Race Total 1,280,060
Office of the Secretary of StateRace Summary Report
2014 Republican Party Primary Runoff
5/27/2014
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Attorney General
Dan Branch REP 269,098 36.59%
Ken Paxton REP 466,407 63.41%
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Race Total 735,505