In the midterms last week, the Republicans had performed significantly weaker than expected. The Democrats' success is notable because the midterms, halfway through a US President's term in office, are traditionally used by voters to punish the President's party. In view of the high inflation and poor poll numbers for Biden, the Republicans had bet on a landslide victory known as the “red wave”.
With the majority now won in the House of Representatives, the Republicans could initiate parliamentary investigations into Biden or his confidants. Without a majority in the Senate, however, they cannot get legislation through Congress that contradicts Biden's agenda, such as abortion or climate protection. Nor can they block the appointment of judges, ambassadors or government representatives.