Barack Obama will officially announce Sonia Sotomayor as his choice to replace Justice David Souter on the Supreme Court at 10:15 am ET, according to Jake Tapper’s Twitter report.  Given the numerical advantage Democrats hold in the Senate, most presume Obama will have no problem getting anyone he picks confirmed into the seat.  However, Senator Jon Kyl (R-AZ) told Chris Wallace on Sunday that Obama could provoke him into starting a filibuster, as quixotic as that may be:

The Senate’s No. 2 Republican on Sunday refused to rule out a filibuster if President Barack Obama seeks a Supreme Court justice who decides cases based on “emotions or feelings or preconceived ideas.”

Sen. Jon Kyl made clear he would use the procedural delay if Obama follows through on his pledge to nominate someone who takes into account human suffering and employs empathy from the bench. The Arizona Republican acknowledged that his party likely does not have enough votes to sustain a filibuster, but he said nonetheless he would try to delay or derail the nomination if Obama ventures outside what Kyl called the mainstream.

“We will distinguish between a liberal judge on one side and one who doesn’t decide cases on the merits but, rather, on the basis of his or her preconceived ideas,” Kyl said.

At issue is Obama’s promise to choose a nominee who uses “life experiences” and “empathy” to decide outcomes in court cases, rather than the law.  And Kyl may have some company across the aisle on this same point:

Ben Nelson has to answer to Nebraska, a state so red it went for John McCain over Obama by 15 points.  Nelson also opposes Card Check, along with a few other red-state Democrats in the Senate, but joining a filibuster on an Obama appointment will be much less forgivable than a nay on EFCA.  Both Kyl and Nelson were part of the Gang of 14 that kept Bill Frist from exercising the “nuclear option” of eliminating filibusters on judicial appointments, and Nelson’s threat to join a filibuster if Obama appoints an activist is somewhat ironic, under those circumstances.

Does Nelson really mean it?  I don’t know that he gains much by issuing the threat alone.  It sends a signal that Obama won’t get an easy ride for the most obnoxious appointees to the bench, which leaves out Dawn Johnsen and Harold Koh down the road, but may not have much effect on the Sotomayor pick now.  We should watch Nelson’s reaction to Sotomayor and gauge then his seriousness in blocking activists from the Supreme Court.

Update: Senate Minority Leader Mitch McConnell issued this routine statement:

“Senate Republicans will treat Judge Sotomayor fairly. But we will thoroughly examine her record to ensure she understands that the role of a jurist in our democracy is to apply the law even-handedly, despite their own feelings or personal or political preferences.

“Our Democratic colleagues have often remarked that the Senate is not a ‘rubber stamp.’ Accordingly, we trust they will ensure there is adequate time to prepare for this nomination, and a full and fair opportunity to question the nominee and debate her qualifications.”

That’s standard boilerplate, and it says little about Republican intentions.  McConnell could easily have issued a similar statement about a Bush nominee.  It’s not as though Sotomayor was a surprise pick; Republicans had plenty of time to prepare themselves for her selection.  This may indicate that the GOP wants to test the waters before committing to an all-out war over Sotomayor, or choosing to paint her as an extremist as grist for the midterms.