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Political expression 
One weakness of such an approach is that effective political parties are usually coalitions of factions or advocacy groups. Bringing together political forces based on a single intellectual or cultural common denominator can be unrealistic; though there may be considerable public opinion on one side of an argument, it does not necessarily follow that mobilizing under that one banner will bring results. A defining issue may indeed come to dominate one particular electoral campaign, sufficiently to swing the result. Imposing such an issue may well be what single-issue politics concern; but for the most part success is rather limited, and electorates choose governments for reasons with a broader base.
Single-issue politics may express itself through the formation of a single-issue party, an approach that tends to be more successful in parliamentary systems based on proportional representation than in rigid two-party systems (like that of the United States). Alternatively, it may proceed through political advocacy groups of various kinds, including Lobby groups, pressure groups and other forms of political expression external to normal representative government. Within a broad-based party it may be the concern of a single-issue caucus.
Very visible as it was in Western democracies in the second half of the twentieth century, single-issue politics is hardly a new phenomenon. In the 1880s, the third government of William Ewart Gladstone made British politics in practical terms single-issue, around the Home Rule Bill, leading to a split of the Liberal Party.
Groups and voters 
Single-issue politics are a form of litmus test; common examples are abortion, taxation, animal rights, environment, and gun politics. The National Rifle Association in the United States, which has only one specific interest, is an example of a single-issue group. What differentiates single-issue groups from other interest groups is their intense style of lobbying.
The term single-issue voter has been used to describe people who may make voting decisions based on the candidates' stance on a single issue (e.g. "pro-life" or "pro-choice", support for gun rights or gun-control). The existence of single-issue voters can give a distorted impression: a candidate's overall views may not enjoy the same support. For example, a person who votes for a socially conservative Republican candidate, based solely on his or her support of gun rights, may not necessarily share the candidate's other views on social issues, such as abortion or family values.
Single-issue parties 
A single-issue party is a political party that campaigns on only one issue. Such a party is rarely successful in gaining elected office.
It is generally believed that single-issue parties are favoured by voluntary voting systems, as they tend to attract very committed supporters who will always vote. Through systems like instant runoff voting and proportional representation they can have substantial influence on the results of elections. First past the post voting systems tend to nullify their influence.
In instant-runoff electoral systems which allow unsuccessful parties to designate where their votes are redistributed, single-issue parties may be formed as a way to funnel more votes to another candidate with quite different policies. For instance, in the New South Wales state election, 1999, one candidate who received just 0.2% of the primary vote achieved the quota of 4.5% required to win a Legislative Council seat after receiving preferences from a wide range of minor parties (including both the 'Gun Owners and Sporting Hunters Rights Party' and the 'Animal Liberation Party'); MLC Lee Rhiannon accused many of these parties of being nothing more than fronts..
Some examples of single-issue parties are the party formed to protest against the increase in politician wages, the Bloc Québécois party in Canada, formed to call for the separation of Quebec, and the Party for the Animals, which gained two seats in the Dutch parliament in 2006.
Green parties and cannabis political parties, which exist in a number of countries, are explicitly based around single issues. These parties often evolve to adopt a full platform, however, and most Green parties and today's Bloc Québécois have full platforms. In the case of the Bloc Québécois, separatism is today a secondary issue.