WASHINGTON, D.C. - Senate leaders are now getting last-minute rules in place for President Donald Trump’s impeachment trial. Opening arguments are expected to start on Tuesday.

But will the trial include witnesses? That’s still a contentious issue on capitol hill.

Sen. Brian Schatz (D-Hawaii) is among the Democrats who want as many witnesses as possible during the Senate trial.

“Trials have witnesses,” Schatz said. “That’s the bottom line.”

But it’s unclear exactly if – or how many – witnesses could testify. Democrats are still pushing for top current and former White House officials to take the stand. Their wish list includes former National Security Advisor John Bolton, and others with first-hand knowledge of the phone call between Trump and Ukrainian President Volodymr Zelensky, the call at the heart of inquiry that led to Trump’s impeachment.

“Every impeachment trial, whether it was a presidential impeachment or an impeachment of a federal judge, in the United States Senate has always had both a documentary record and physical witnesses and depositions,” Schatz said.

Across the aisle, Senate Republicans remain torn about more witness testimony. Sen. Patrick J. Toomey (R-Pa.) is open to that idea. He wants to hear opening arguments, to see if witnesses are actually needed.

“I’m not sure so much that my colleagues want to hear from John Bolton as they want to force Republicans in tough Senate to vote on whether or not to hear from John Bolton,” Toomey said Wednesday.

The trial is expected to take several weeks, limiting time on the campaign trail for Democratic senators running for president. Because the trial is expected to take several weeks, it will likely overlap Trump’s State of the Union address on February 4.

“If it were so important to hear from John Bolton, then the House would have litigated this,” Toomey said.