NEWARK, N.J. (AP) — Jury selection in the corruption trial of U.S. Sen. Bob Menendez concluded Tuesday with several panelists seated after the first day of questioning by attorneys.

Several jurors were seated by the end of the day. The process will continue Wednesday to pick the 12 jurors and four alternates who will sit on the trial. Opening arguments are scheduled for Sept. 6 for what is expected to be a two-month trial.

Menendez was indicted in 2015, charged with accepting campaign donations and gifts, which included vacation trips to Paris and the Dominican Republic from eye doctor Salomon Melgen. In exchange, according to the indictment, Menendez used his position in Congress to lobby for Melgen's business interests.

Melgen, who lives in Florida, and Menendez have argued in court papers that the gifts and donations were innocent and that there was no bribery agreement. Menendez also claims his actions were legitimate legislative duties.

Tuesday began with Menendez and Melgen pleading not guilty in a closed hearing to a superseding, or updated, indictment that was filed last fall by the government after U.S. District Judge William Walls dismissed two bribery counts against each defendant.

While the proceeding was routine, the exclusion of the public and media was not. Except in rare cases, such as when the identity of a government informant must be kept secret, defendants enter guilty or not-guilty pleas in open court.

Walls didn't give an explanation for closing the courtroom.

Melgen was convicted in April on multiple counts of Medicare fraud in a separate trial. Menendez wasn't implicated in that case, but part of the indictment charges him with interceding on behalf of Melgen in a Medicare dispute.

The government's case centers on meetings and interactions Menendez had with, among others, then-Health and Human Services Secretary Kathleen Sebelius and acting Medicare administrator Marilyn Tavenner.

Jurors will have to weigh whether those fall under the category of "official acts" under a law whose definitions have shifted in the wake of a 2016 Supreme Court ruling in the case of former Virginia Gov. Robert McDonnell.

If Menendez is convicted and steps down or is forced out of the Senate before Gov. Chris Christie leaves office Jan. 16, the Republican would pick a successor. It would take a two-thirds majority vote to remove him from the Senate. His seat is up for election next November.

Democratic gubernatorial nominee Phil Murphy has a large lead in polls ahead of his Republican challenger in the race to replace Christie.