A House committee controlled by Democrats wants to see secret documents that it says could lead to another impeachment inquiry.
Chief justice John Roberts returns to the Supreme Court facing cases on abortion, immigration, gay rights, gun rights and Donald Trump's tax records.
Witnesses could be summoned. Documents could be demanded. Executive privilege could be claimed. Democrats may ask Chief Justice John Roberts for help.
Questions from senators represented a new phase in the impeachment trial. On Friday, the central issue of witnesses and documents will be addressed.
For a government prone to partisan squabbling, a buttoned-down, by-the-book chief justice presiding over the impeachment trial is a welcome change.