A special election is called when a legislative seat becomes vacant between regular election cycles due to death, resignation, expulsion, or other causes. In the U.S. House of Representatives, Article I, Section 2 of the Constitution requires that vacancies be filled by election—governors cannot appoint replacements as they can for some Senate vacancies under the 17th Amendment. Special elections typically have much lower voter turnout than general elections, which can amplify the effects of motivated partisan bases. Political scientists treat patterns across many special elections as leading indicators of the national political environment heading into the next general election.