Clause 1. The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof; but the Congress may at any time by Law make or alter such Regulations, except as to the Places of chusing Senators.
The Constitution generally leaves it up to the states to organize congressional elections, but gives Congress the power to set new rules for federal elections as it sees fit. In 1842, Congress passed an important law requiring single-member district elections in every state, standardizing congressional election practices nationwide. The same law set one standard Election Day—the Tuesday after the first Monday in November—throughout the country. We still use the same Election Day today.
Clause 2. The Congress shall assemble at least once in every Year, and such Meeting shall be on the first Monday in December, unless they shall by Law appoint a different Day.
This clause requires at least one session of Congress to meet each year. The 20th Amendment, passed in 1933, moved the standard opening day from the first Monday in December to January 3.