Senator Lamar Alexander really knows how to drain the suspense from an impeachment fight, doesn’t he?

Friday was supposed to be the big showdown in the Senate’s trial of President Trump — the long-awaited skirmish over whether to call for new witnesses and documents. To hit the 51-vote threshold, four Republicans needed to vote “aye” with the Democrats.

The chances of this had seemed negligible until last Sunday, when The Times reported that, in a forthcoming book, John Bolton, the former national security adviser, shares that the president told him that the security aid for Ukraine was linked to Ukraine announcing the corruption inquiries Mr. Trump sought.

Since a central piece of the president’s defense has been to complain about the dearth of witnesses who spoke directly with the president about Ukraine, the revelations cranked up the heat on Senators to hear from Mr. Bolton. Mr. Alexander was considered one of the Republicans most likely to grow a spine and cross the aisle.