Obama and the D leadership motivated the R's. Compare the makeup of the White House, Senate, House and Supreme Court in a relatively short period of time:
January 2009
President -- D
House -- Controlled by D's
Senate -- Controlled by D's
Supreme Court -- Not Conservative
October 2018
President -- R
House -- Controlled by R's
Senate -- Controlled by R's
Supreme Court -- Conservative
January 2009
President -- D
House -- Controlled by D's
Senate -- Controlled by D's
Supreme Court -- Not Conservative
October 2018
President -- R
House -- Controlled by R's
Senate -- Controlled by R's
Supreme Court -- Conservative