In 1980 Ronald Reagan convincingly won the presidency against Jimmy Carter, and also tipped the Senate. But the democrats maintained control of the House and Tip O’Neill remained speaker. That meant a lot of people voted for Reagan, but then voted democratic down ballot. They could do this knowing bipartisanship was possible - that the country had a coherent population, and differences were not so wide that people would refuse to work together.
Reagan was able to push his tax reduction plan through Congress. Tip O’Neill basically said ‘this is what the people voted for, so we will work with you.’ That could not happen today.
The US electorate is balkanizing because of too much immigration too fast - which is exploited by unscrupulous politicians. We will probably not see the kind of bipartisanship of the early 1980s again in our lifetimes - if ever. And this is why a 1924 style moratorium on immigration is necessary, coupled with aggressive assimilation policies and deportations of those who don’t really want to be American. And it’s why birthright citizenship is a disaster in present circumstances.