The U.S Congress is a bicameral (”two-chambered”) legislature, consisting of the House of Representatives and the Senate. The House of Representatives is based on population, with 435 Representatives each representing a local district that’s supposed to be relatively equal in population. The Senate is not based on population, so that every state has exactly two Senators.
Democrats taking power in the House has a lot of important consequences:
- Veto power over legislation. This is the most straightforward consequence. Since legislation has to be approved by both the House and Senate, no legislation is going to happen for the next two years without approval from the Democratically-controlled House. This is especially true for taxation, spending, and budgets, since revenue bills have to start in the House.
- Agenda-setting. Even though they can’t pass laws on their own, the House still has the ability to put issues on the national political agenda by passing bills through the House or attaching them as amendments to Senate legislation, and then forcing both/either Trump or Republicans in the Senate to take a position. This includes stuff like the DREAM Act, raising the minimum wage, women’s right to choose, voting rights, and on and on.
- Subpoena/investigative powers. Both the House and Senate have a number of committees, which have powers to investigate pretty much anything they want to. These powers include the power to issue subpoenas to compel witnesses to testify or disclose documents, the power to hold people in contempt (i.e, fine and/or jail them) for non-compliance, or to charge them for lying to Congress in addition to perjury if they don’t tell the truth. For the last two years, Republicans have refused to use these powers in relation to a very long list of things, pretty much every scandal that you’ve heard about from the 2016 campaign through the whole of the Trump Administration. Now, Democrats can use their investigative powers to hold the Trump Administration and Trump himself accountable under the law.
- Impeachment. While Republican control of the Senate makes convicting and removing Trump from office unlikely, it is quite possible that in the investigations of the Trump Administration by Congress or the Mueller investigation, that they turn up enough to charge the president with obstruction of justice, abuse of power, and/or whatever colluding with the Russian government actually works out to in the law. Then the rest is up to the Senate, and ultimately the American people in 2020.