It increasingly appears that the reason why Harriet Miers' nomination was withdrawn today was because of the underwhelming support -- and indeed opposition -- of conservative Republican Senators. CQ Today's Midday Update (a free email service) has the story.

President Bush made the decision to withdraw the Supreme Court nomination of White House counsel Harriet Miers, but the impetus came from Senate Republican leaders.

According to a GOP leadership aide, the entire leadership team held a dinner meeting at the Capitol last evening. On the menu: an “honest discussion about where the nomination stands.”

Afterwards, Majority Leader Bill Frist, R-Tenn., relayed their assessment to White House chief of staff Andrew Card. “I gave an accurate reflection of where the nomination stood,” he told reporters today.

GOP aides say he conveyed a fairly grim assessment of Miers’ chances if the White House did not turn over documents relating to her legal advice to the president.

Marc Ambinder reports along similar lines for Hotline on Call.

The tipping point came within the past several days. GOP Senators privately communicated to WH CoS Andy Card that unless they had access to hard evidence that Miers was conversant in constitutional issues, there was no way she would be confirmed. Her performance in private meetings was weak, at best, these senators told Card. Throughout the day yesterday, says a senior Senate aide, there were "conversations throughout the day at the staff level." Late yesterday, Senate Maj. Leader Bill Frist (R-TN) called Card and told him in no uncertain terms that Miers would probably not be confirmed. An aide: "He provided frank assessment of situation in the Senate. [The] lay of land on committee." After that call, according to White House sources, Bush and Card met privately with Miers, and they decided jointly that preserving WH privilege on documents was too important a principle to risk. Miers officially informed Bush at 8:30 pm ET. As late as 8 p.m., one White House aide said the WH counsel's office was rushing to finish a revision to the Senate Judiciary Committee questionnaire. (It arrived after 11:00 pm ET). Word began to spread through conservative Washington last night. The White House office of political affairs notified allies at about 8:30 a.m ET this morning but swore them to secrecy until the White House released the President's statement.