TX has not elected a Democrat to a US Senate since 1988 (Bentsen-D got re-elected to a fourth term), Democrats have not won any statewide election in TX since 1990/1994. Ann Richards-Governor-1990,Bob Bullock-Lt Governor-1994,Dan Morales-Attorney General-1994,John Sharp-Comptroller-1994, Garry Mauro-Land Commissioner-1994, and Jim Hightower-Agriculture Commissioner-1986.
Hightower lost re-election in 1990 to Rick Perry-R.
Mauro gave up the Land Commissioner position to run for Governor in 1998 against George W Bush-R (was replaced as by David Dewhurst-R)
Sharp gave up the Comptroller position to run for Lt Governor in 1998 against Rick Perry-R (was replaced by Caroline Keeton-R)
Morales gave up the Attorney General position in 1998 was replaced by John Cornyn-R.
Bullock gave up the Lt Governor position in 1988 was replaced by Rick Perry-R.
Richards lost re-election in 1994 to George W Bush.
Republicans have won every statewide election in Texas since 1998- most of it had to do with Bush's popularity in TX from 1994 to 2008.
Losing Democratic US Senate nominees in TX-
Victor Morales-1996-got 44 percent against Phil Gramm-R,
Ron Kirk-2002 got 43 percent against John Cornyn-R,
Rick Noriega-2008 got 43 percent against John Cornyn-R,
Paul Sadler-2012 got 41 percent against Ted Cruz-R.
Republicans margin of victory in TX during the 2016 Presidential election was much narrower than 2012. Beto O'Rourke-D -2018 is a stronger candidate than Paul Sadler-D- 2012. The only way O'Rourke could defeat Cruz is a Conservative Independent running in the November General Election and Democrats contesting low level statewide elections in TX.