have decried the tendency of most House seats to become safe seats, decreasing the number of contested seats in every cycle. This is due to a variety of disparate factors. The first involves migration patterns in the United States. Works by the Pew Research Center and author Bill Bishop show how like-minded voters will gravitate toward communities with shared values. Cities such as Berkeley, California, and Ogden, Utah, consistently elect members of one party due to their populations. The second factor revolves around partisan gerrymandering. Many congressional districts are gerrymandered – drawn by state legislatures to be all but unwinnable for the district's minority party (with only a handful of districts, either in strong pockets of support or in order to avoid court challenges of racial discrimination, allocated to the minority party), or with districts split through bipartisan agreements to ensure incumbent protection (such as maintaining heavily Democratic urban districts and heavily Republican rural districts). Specific U.S. States, congressional districts, and senate seats since 2000 are sometimes referred to as "solid blue" (Democratic Party) or "solid red" (Republican Party) after the use of these colors in television maps on election night. The Cook Partisan Voting Index rates congressional districts on how strongly they lean towards either major party. As of the 2022 redistricting, California's 12th district is the most Democratic at D+40, while Alabama's 4th district is the most Republican at R+33. Other examples of a safe seat for the Democrats is California's 12th congressional district, which currently covers most of the city of San Francisco. This district and its predecessors have been in Democratic hands without interruption since 1949. Its current representative, former House Speaker Nancy Pelosi, was most recently reelected with 77.6 percent of the vote. Safe Republican seats include Tennessee's 1st congressional district and Tennessee's 2nd congressional district, which are located in the eastern part of the state. Both districts have been held by Republicans or their predecessors (except for two terms in the 1st) since 1859, despite the South's shift from being monolithically Democratic to being heavily Republican. Because American representatives are generally residents of the constituency which they represent, it is much less common for aspiring politicians to select safe seats to represent. In fact, an aspiring politician may instead want to prove oneself by winning a swing seat and thus show they have the capability of winning a close-fought election, thus making the candidate