That results in a 47 percent efficiency gap heavily favoring Democrats, but both races were close, and if fewer than 5,000 votes had switched in either district, the efficiency gap would be almost even.
The AP also calculated efficiency gap scores for the U.S. House elections, though experts caution those measurements are less statistically meaningful in states with few districts.
"There's one answer for that, one word: gerrymander", said Terry Madonna, director of the Center for Politics and Public Affairs at Franklin & Marshall College in Lancaster, Pennsylvania.
University of Georgia political science professor Charles Bullock said the large number of uncompetitive districts in his home state might be due less to gerrymandering than to naturally segregated demographics, with Democratic-inclined black residents living in different areas than Republican-leaning white voters.
Toscano said opposition to Trump is so strong that it's overcome the reluctance Democratic candidates have had in the past to compete in a district with Republican-friendly boundaries. Republicans captured 67% of the overall Congressional vote in 2016, but won all four House seats that year.
Dingell said Republicans should be anxious, despite questions about House Minority Leader Nancy Pelosi (D-Calif.).
Yet there also were some districts that didn't appear to follow the Republican proposal, said former citizens' commission member Nick Myers, who now is secretary of the Missouri Republican State Committee. All had districts drawn by Republicans after the last Census in 2010.
Incumbent Republican Rep. Mia Love won that district in November with 54 percent of the vote, defeating Democrat Doug Owens.
Utah is one of the most conservative states in the country, and Republicans have long controlled the state Legislature. "Their problem is weak candidates who run poor campaigns based on bad ideas, not the districts", said Christopher West, spokesman for House Speaker Bill Howell, R-Stafford. Sometimes, delegates wanted the boundaries changed to draw out a potential primary challenger, Jones said. The efficiency gap scores show Republicans picked up at least two excess seats each in MI and North Carolina. Republicans may have won an extra congressional seat over what would have been expected based on the average vote share around the state that shows a large so-called "efficiency gap". "We met the criteria the Supreme Court required us to meet".
In Texas, Republicans gained almost four excess congressional seats compared to projections from a typical votes-to-seats ratio, according to the AP's analysis.
Democrats and redistricting drafters in Nevada reject the notion of a Democratic advantage, pointing out that Republicans won control of the Legislature in one of the three elections since the current district lines were implemented.