UPDATE (9:00 PM CDT): Alex Koppelman over at Salon’s War Room reports that Sara Taylor will at least show up to a Senate Judiciary Committee hearing on Wednesday.  It isn’t clear whether she will testify or invoke her Fifth Amendment privilege.  It is not clear whether Miers will appear before the House Judiciary Committee on Thursday. -END-

In the continuing investigation over the firings of U.S. attorneys as a partisan political effort by the Bush Administration, President George Bush asserted executive privilege and will not allow two aides to testify to the Senate Judiciary Committee, even though they have been subpoenaed by Congress.

Harriet Miers, former White House Counsel and Supreme Court nominee, as well as Sara Taylor, an Iowa native and former White House political director, were subpoenaed by Congress on June 13 in an effort to determine whether the firings of eight U.S. Attorneys were politically charged.  Some have alleged the firings were part of an effort to stymie probes of Republican political officials or prompt investigations of Democrats.  Thousands of pages of documents have already been turned over to Congress as part of their ongoing investigation.

Taylor left her job at the White House at the end of May, citing a desire to work in the private sector.

Taylor is a graduate of Drake University and former national co-chairman of the College Republicans.  She began work on Bush’s presidential campaign in 1999 and soon worked her way up to deputy political director, working directly under Bush aide Karl Rove.  She is also the daughter of former state legislator Ray Taylor.

During the 2004 election, Taylor helped create the Bush-Cheney microtargeting strategy that was a critical voter turnout tool.  The campaign analyzed voter spending patterns and then developed lists of potentially sympathetic voters. Those voters were then targeted for direct mail and other advertising. The data-mining techniques are credited with giving Republicans a decisive turnout advantage in the 2004 election.

In documents and testimony provided to Congress, Justice Department officials have revealed that the White House seemed to be directing the firings of U.S. Attorneys.  Karen Tumulty of Time Magazine reported in May:

“In private testimony that is being released this afternoon by the committee, Alberto Gonzales’s former Chief of Staff Kyle Sampson told investigators that Gonzales himself initially resisted the idea of bypassing the Senators from Arkansas to install Karl Rove protege Tim Griffin as U.S. Attorney for the Eastern District of Arkansas. Pressure to do it, he suggested, was coming from officials at the White House-specifically, White House political director Sara Taylor, her deputy Scott Jennings and Chris Oprison, the associate White House counsel. Sampson described himself and Goodling as “open to the idea,” which is not the same as instigating it.”

Bush’s assertion of executive privilege is sure to rile Congressional Democrats who believe their investigation is being blocked by unlawful or unjustified attempts to assert privilege.  The White House Counsel, Fred Fielding, counters that they have offered up Taylor’s testimony in an informal and off-the-record sit-down with members of Congress.

Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., said yesterday on CNN that he would seek contempt citations against the president should he again assert executive privilege and direct Taylor and Miers not to testify.

“I haven’t heard anything from Mr. Fielding or anybody else at the White House that would justify a claim of executive privilege,” Leahy said. “[Taylor] sent something like 60,000 e-mails on the Republican National Committee account, not e-mails to the president, but political e- mails while she was there.”

The showdown between the two branches over the assertion of executive privilege and contempt citations would effectively create a constitutional situation not seen since the days of Watergate, when President Richard Nixon asserted executive privilege on recorded communications inside the White House.  The Supreme Court overturned the assertion of privilege and Nixon eventually resigned from office.