Party leaders encourage individuals who they believe will be strong candidates to run for office, focusing on those who have positions compatible with those of the party leadership and some professional experience that can be presented as relevant. Proven ability to win elections is a plus, and many individuals move up the ladder from city or county office to run for state office or to compete for a seat in Congress. Parties tend to favor officeholders running for reelection unless they have done something to alienate or antagonize party leadership or voters. While party leaders try to ensure that their favored candidates win the nomination, their control is limited. If candidates are nominated through primaries, party leaders may only endorse, or give official party approval to, a particular candidate for office. That candidate would have to win the primary to be eligible to run in the general election. Party control over candidates is limited in another way—any individual can choose to run for any office and, by meeting whatever standards are required for a particular office, be listed on the primary ballot.
Once nominees are chosen, parties at all levels—national, state, and local—work to help them with the election. These efforts include sponsoring campaign events, paying for advertisements, and assisting candidates with fundraising and advice on campaigning. Parties may focus their efforts on supporting their candidates in key races, particularly if they see an opportunity to defeat an incumbent from the other party who they believe is vulnerable or to capture or retain a seat that has become open due to the retirement of an incumbent. Parties maintain databases of members and use active members to make phone calls to encourage voting in an upcoming election and to make sure they go to the polls on election day. For much of this effort, parties rely on the voluntary work of those each committed member, who can be called a party activist, a person who works to advance a political party's interests.
Political parties are also active between elections. A political party spends considerable time making sure that its officeholders' views and records are publicized to the electorate—typically through the use of messages sent by traditional mail or email. Parties also organize fundraisers to help meet expenses and to have resources for the next round of elections.