The Senate impeachment trial of President Donald Trump — only the third in U.S. history — is scheduled to get fully underway Tuesday, with Democrats and Republicans potentially clashing over whether to call witnesses.

The proposed rules for the trial, which Senate Majority Leader Mitch McConnell, R-Ky., released Monday evening, are similar but not identical to the format of President Bill Clinton’s impeachment trial in 1999. McConnell’s rules would set aside up to four hours of debate, equally divided between both sides, on whether there should be subpoenas for witnesses or documents, and then the full Senate would vote on the issue.

Read the rest of the story at NBC News.