Federal authorities have arrested more than two dozen foreign nationals Monday in California, who authorities said have illegally registered and voted in U.S. elections.

The statewide sweep is part of a Trump administration effort to root out noncitizen voting ahead of next month's midterm elections, even though data shows that the problem is incredibly rare, difficult to prove and has not been shown to change the outcome of races.

The arrests also reflect a further escalation in a simmering voter roll fight between the federal government and California that came into focus last week when the Justice Department sued the state and later warned that local election workers who knowingly process or tabulate ballots submitted by noncitizen voters are at risk of investigation and potential prosecution.