Move is latest attempt to challenge states with competitive midterm races that could determine control of Congress

The Trump administration on Monday asked Washington state to set aside any ballots received from more than 400 people it alleges are registered to vote without US citizenship, less than two weeks after making a similar demand in California.

The announcement is the latest sign of the administration’s attempts to sow doubts about the election or its outcome in states with races that will help determine control of the US Senate and House.

In a letter to the Washington secretary of state, Steve Hobbs, the justice department said it had identified 1,500 votes cast by more than 400 people in prior elections. It asked the state to set aside any ballots they might cast in next month’s midterm elections until state officials can confirm they are legally eligible to vote. The state has more than 5 million registered voters, and the state issues mail ballots to all of them.