identification becomes somewhat formalized when a person runs for partisan office. In most states, this means declaring oneself a candidate for the nomination of a particular party and intent to enter that party's primary election for an office. A party committee may choose to endorse one or another of those who is seeking the nomination, but in the end the choice is up to those who choose to vote in the primary, and it is often difficult to tell who is going to do the voting. The result is that American political parties have weak central organizations and little central ideology, except by consensus. Unlike in many countries, the party leadership cannot prevent a person who disagrees with basic principles and positions of the party, or actively works against the party's aims, from claiming party membership, so long as the voters who choose to vote in the primary elections elect that person. Once in office, elected officials who fail to "toe the party line" because of constituent opposition to it, and "cross the aisle" to vote with the opposition, have (relatively) little to fear from their party. An elected official may change parties simply by declaring such intent. At the federal level, each of the two major parties has a national committee (See, Democratic National Committee, Republican National Committee) that acts as the hub for much fund-raising and campaign activities, particularly in presidential campaigns. The exact composition of these committees is different for each party, but they are made up primarily of representatives from state parties and affiliated organizations, and others important to the party. However, the national committees do not have the power to direct the activities of members of the party. Both parties also have separate campaign committees which work to elect candidates at a specific level. The most significant of these are the "Hill committees", which work to elect candidates to each house of Congress. State parties exist in all fifty states, though their structures differ according to state law, as well as party rules at both the national and the state level. Despite these weak organizations, elections are still usually portrayed as national races between the political parties. In what is known as "presidential coattails", candidates in presidential elections become the de facto leader of their respective party, and thus usually bring out supporters who in turn then vote for his party's candidates for other offices.