Why it matters: The board writes in its editorial that its decision to endorse two candidates is a major break with convention that's intended to address the "realist" and "radical" models being presented to voters by the 2020 Democratic field.
Senators will almost certainly get to vote on whether or not to call impeachment witnesses. The resolution laying out the rules of the trial, which will be presented Tuesday, is expected to mandate that senators can take up-or-down votes on calling for witnesses and documents.
Yes, but: Those votes won't come until the House impeachment managers and President Trump's defense team deliver their opening arguments and field Senators' questions.
Trump officials say they feel especially bullish about one key argument against calling additional impeachment witnesses: It could compromise America's national security.
The big picture: People close to the president say their most compelling argument to persuade nervous Republican senators to vote against calling new witnesses is the claim that they're protecting national security.