I have heard that the coattails effect is where a candidate gets elected because the president is popular in the area they want to represent. I feel like it is getting stronger over time. Ticket splitting appears to be rarer in Democratic voters:

For example, in 2012 and 2016, over 90 percent of districts voted for the same party for the president as the House. That increased further. In 2016 and 2020, all but one Senate race went the same way from the presidential level. House:

Governor (there are plenty of outliers):

Has the coattails effect become a stronger force?