More than people realize. Between the Civil War and this century, the Texas delegation to the US House of Representatives was Majority-Democrat. We had a Democratic governor just 3 Governors ago.

But in 2003 the Texas legislature went majority-Republican for the first time in over a century, and the first thing they did was massively gerrymander the state just a year after it had been redistricted for the 2000 census.

In the 2002 election, 17 Democrats and 15 Republicans were elected to the US House. Following the redistricting, the 2004 election had 21 Republicans and 11 Republicans elected to the House.

With a single map change they went from a minority to a 2:1 majority.