There's a natural ripening process. The Senate is almost never in a rush. In normal times, any one of 100 senators has the power to launch a filibuster at any moment. Filibusters are not permitted during an impeachment trial, but conviction takes a two-thirds majority, an impossible threshold without an extraordinary degree of bipartisan cooperation. Because of such rules, the majority must be circumspect in its treatment of the minority, and the minority should be appreciative of this deference.
Parties often agree to disagree, but open breaches are rare.
And besides, nobody wants to look bad. By the time the Senate convened Wednesday, it quickly became apparent that one bipartisan plan to hold an abbreviated trial, with a quick vote to identify whether there were the votes to convict, was in trouble. Lott had appeared to favor it in the interests of bipartisanship and a quick end to an unpleasant task, but Senate conservatives and conservative groups that make up a significant part of the GOP's base voters were holding out for witnesses and an extended proceeding. Hopes for a quick deal rose again Wednesday night when Republican and Democratic negotiators for the Senate met with the House prosecutors and White House lawyers at the Capitol. The White House offered to stipulate to the evidence compiled by independent counsel Kenneth W. Starr in exchange for a quick trial without witnesses.