Cornyn's ad quotes some magazine or organization saying he is the second most conservative member of the Senate. I looked up his 2012 ranking (the most recent ranking available) by the American Conservative Union based on the votes on 25 Senate bills. By the ACU, Cornyn is tied in 2012 for 16th most conservative senator with four other senators. And get this, by the ACU's 2012 ranking John McCain is more conservative than Cornyn.
I should note that the ACU rankings on 25 votes that I cited above were from the second session of the 112th Congress.
The ACU is off its rocker