Congressman Steve Scalise was readmitted to the Intensive Care Unit at MedStar Washington Hospital Center Wednesday night.
The hospital said his admission was due to new concerns for infection.
Scalise is listed as serious condition.
Scalise was shot in the hip and went through surgery previously for his wounds.
The man who carried out the attack, James Hodgkinson, 66, from Belleville, Illinois, was shot dead by police after opening fire, authorities have said.