The US experts: Now the Democrats are gaining a lot of influence

And a heavy setback for President Donald Trump, who will find it much more difficult to get his policies through.

"The president needs to correct himself"

Emma Ricknell, political scientist at the Linnaeus University, notes that the Democrats with their newly won majority get "extensive power" to be able to push through legislation.

- Many different possibilities to either reform existing legislation or introduce new ones. In addition, Congress decides on the budget, which is a huge power to hold and which the president needs to comply with, she says.

The Senate also has the power of appointment when it comes to approving, for example, federal judges, which means that Democrats can block appointments of judges to the Supreme Court and other important posts. They can also block new attempts by the president to impose tariffs on different countries.

But the American system is based on separation of powers:

- And when Congress has passed a law, the president must sign it. So it is likely that many laws that they pass will encounter patrols when they get to the White House, says Dag Blanck, professor of North American studies at Uppsala University.

Trump has already said he will be "Mr. Veto" and use his veto power to stop proposals from being voted on.

In other words, it could get messy in American politics during the two years that remain of the term.

- But if you, as president with a fairly compact opposition in Congress, are to get something that is a long-term policy through, then you have to sit down at the negotiating table, says Ricknell.

- Presidential orders can be torn up the day a new president sits in the White House. It is not the same as legislation.

Possible investigations

Congress also has an important role in controlling what the president does.

As soon as the new assembly has assembled in January, Dag Blanck therefore believes that investigations, committee hearings and investigations will begin.

- People will claim that there are a lot of problems, corruption and that various ministers have done wrong things.

In addition to investigating the Trump administration, impeachment can also be brought.