How often partisans cross over, by office

Weighted share of party identifiers (leaners included) casting a major-party vote for the other party, by office and year.

President Senate House
Mid-century the three offices moved together (about 17–18% defection each). Through the 1980s and 90s the ladder opened: presidential defection fell to 11.5% while House defection climbed to 21.2% — the golden age of the split ticket. Since then every line has fallen toward the presidential floor; by 2024 the spread is almost gone (5–7%). Source: ANES, weighted.

Cross-pressured partisans cross over more — especially down-ballot

Weighted defection rate, pooled 1976–2024, by office and whether the partisan is stranded in an opposite-leaning state.

A stranded partisan defects at the Senate level 19.3% of the time against 10.2% for the comfortable, and at the House 19.9% versus 11.5% — gaps of 9 and 8 points. At the presidential level the gap is half that. Source: ANES + MIT state returns, weighted.