Things began to change in the 1980s. The primary individual credited (or blamed) with souring relations between Democrats and Republicans in Congress was Newt Gingrich (R-GA).
Gingrich, elected to the House in 1978, took an aggressive approach to partisan politics, frequently attacking Democratic leadership and accusing them of corruption and mismanagement in a consistently discourteous manner rarely practiced in Congress.
In 1987, he helped orchestrate the Ethics Committee investigation into House Speaker Jim Wright (D-TX), leading to Wright’s resignation in 1989—an unprecedented event that escalated hostility between the parties.
He forbade Republican representatives from meeting Democratic representatives "after hours," which was when they would often hammer out deals away from the public eye and without the need for partisan posturing.
Gingrich took advantage of C-SPAN’s live coverage of House proceedings, using "Special Orders" speeches to attack Democrats, even when the chamber was mostly empty. This led to increased polarization.
He formed of the Conservative Opportunity Society and led this group of young conservative Republicans who aimed to reshape the party’s messaging, often by taking an openly combative stance toward Democrats.
Gingrich’s tactics in the 1980s laid the foundation for the bitter partisanship of the 1990s, culminating in the 1994 Republican Revolution, where he became Speaker of the House and further escalated political warfare. Many historians consider his approach a turning point in modern congressional partisanship.