Sen. Susan Collins (R-Maine) on Friday said that she is working with a group of Republican senators to allow for both President Trump's legal team and the House managers to be able to call witnesses during the impeachment trial.

Collins told the Bangor Daily News that she is working with a "fairly small" group of senators to ensure that an initial resolution on the trial rules allows for witnesses.

"I am hopeful that we can reach an agreement on how to proceed with the trial that will allow the opportunity for both the House and the president's counsel if they choose to do so," she said.

Collins declined to say how many Republicans she is working with, but argued that her colleagues should be "completely open to calling witnesses."

The initial resolution that set out the process for former President Clinton's 1999 impeachment trial did not include a deal on calling specific witnesses. Instead, it laid out how Clinton's legal team and House managers could ask for witnesses as part of the trial.

The 1999 rules specified that after an initial phase of the trial, which included opening arguments from both sides and questions from senators, it would be "in order to make a motion to subpoena witnesses and/or to present any evidence not in the record."

A second resolution that passed along party lines during the 1999 trial subpoenaed three witnesses for closed-door depositions.

Senate Republicans are currently negotiating the specifics of the rules for Trump's trial after Senate Majority Leader Mitch McConnell (R-Ky.) said he had the votes to start the trial without a deal on specific witnesses.

Collins has backed that model. While she's described herself as "open" to calling witnesses, she's repeatedly argued that a decision on who, if anyone, should testify should wait until mid-trial.

Collins is viewed as a key swing vote in the impeachment trial. Democrats need four Republicans to vote with them to compel the administration to hand over Ukraine-related documents and to call witnesses, including former national security adviser John Bolton and acting chief of staff Mick Mulvaney.

House Speaker Nancy Pelosi (D-Calif.) announced on Friday that the House would send over the articles of impeachment next week, paving the way for the Senate to start its trial.