Migrating population is the key to the trend analysis

[ATFFL]

In 3 of those 4 elections a Texan was on the Republican ballot.  The one with out a Texan on the ticket, a 3rd party candidate was from Texas.

Taking it back to 1980, 5 of 6 elections have had a Texan on the Republican ticket.  This is more than likely to skew the numbers in 2 ways.

First, a favorite son is going to get more votes.

Second, such heavy attention frmo teh national party is going to bring more people to the party locally.

You also have to consider the nature of the election.  1988 was a Bush I blowout, so it would have been very hard to be far above his national average, Texas numbers stayed the same and did not move with teh rest of the nation.

1992 saw the vote split heavily with Perot.

1996 saw Perot II who appealed more to Texas Dems than Reps, an oddity for Perot.

2000 was a dead even election anda again Texas numbers did not shift with the national polls, but stayed steady behind the hometown boy.

[ATFFL]

Have you noticed that the governors of MA, CT, NY, and MD  are all REPs.
In MA Bush got 32%. In NYC - 15% despite the GOP mayor.

If you track those states back you will see they got rid of governors who were either scandal ridden, grossly incompetent or began to favor one part of the state too heavily.