Final answer:
Safe districts are created through gerrymandering, which heavily favors incumbents and makes it difficult for other parties to win in general elections.
Step-by-step explanation:
A "safe district" is a district where a majority of voters identify with their member of Congress's party.
Safe districts are created through gerrymandering, which is the manipulation of legislative districts to favor a particular political party or candidate.
One common type of gerrymandering is the creation of safe districts that heavily favor incumbents, making it difficult for challengers from other parties to win in general elections.
In safe districts, the primary elections may remain competitive, but the general elections are usually non-competitive.