Washington (CNN) The trial of Paul Manafort and Rick Gates may begin in spring 2018, Judge Amy Berman Jackson said Friday, meaning the case could push into the summer as midterm congressional election races heat up.

Jackson's proposal for a May 7 start date comes as Manafort's attorneys said Friday they plan to challenge the legal basis of the charges against him, as well as evidence was "improperly obtained" by search warrant and subpoena, including the exceptions the judge made for privileged information.

The attorneys could attempt to change the trial date during a court appearance Monday, Jackson said, if they believe it's too early to set a date or they have scheduling conflicts. However, Jackson made clear she wouldn't allow changes to a trial date once it's finalized.

Manafort and Gates have pleaded not guilty to the nine and eight charges they face, respectively.

Both are currently under house arrest and are due back in court Monday morning.

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