Senate electoral process means although Democrats received more overall votes for the Senate than Republicans, that does not translate to more seats
In the United States, each state gets 2 senators per state, regardless of size. Wyoming has 1/60th the amount of people as California, which means that each Wyoming person has 60 times more influence on the government than the people of California. That’s why millions more voted for Democrats but the Republicans still control the Senate.
Source: Democrats got millions more votes – so how did Republicans win the Senate? | US news | The Guardian