The Constitutional Convention, 1787
The elections for the president of the United States of America have always gotten more attention than any other in this country. This is not surprising, given that the presidency is the only office that the entire country can vote on; and as Alexander Hamilton once said, any individual serving as the president, "from the entire circumstance of his being alone, [is] more narrowly watched and more readily suspected" (Source: Federalist No. 70, with an alternate version saying "from the very circumstance of his being alone"). Your typical member of Congress can put the blame for their own actions on someone else, in other words - usually their fellow members of Congress - more easily than the president can, because they are not watched as closely as a single powerful individual (like the president) is. It is thus natural that the elections for the presidency (held every four years) would be watched more closely than any other elections.
Nonetheless, the elections for the United States Congress are still of importance to this country - as is testified by the part of the Constitution about the powers of the Congress (Article 1, Section 8, to be specific; which has 18 clauses in it); so these elections are held more frequently than the elections for the presidency are. The Constitution actually specifies a shorter term of two years for the members of the House of Representatives at the national level. This means that for this house of Congress, in practical terms, the whole lot of them are up for re-election every two years; and not just every four years (as it is for the presidency). I should note that half of these elections for Congress are held simultaneously with the presidential elections, with the ballot being the same one used to vote for the president. The other half of them are held at the midway point between the two presidential elections (hence the popular name that they have of the "midterm elections," since they're in the middle of the four-year term of the president). The next Congressional elections are in the midterm elections of 2018, although the next leap-year elections coincide with the presidential elections of 2020; so if you do want a say in who your Congressman or Congresswoman is, either one could be a great time to get it.
Constitution of the United States of America