Newsweek:

White House anxiety is mounting over the prospect that top officials-including deputy chief of staff Karl Rove and counselor Dan Bartlett-may be forced to provide potentially awkward testimony in the perjury and obstruction trial of Lewis (Scooter) Libby.

Both Rove and Bartlett have already received trial subpoenas from Libby's defense lawyers, according to lawyers close to the case who asked not to be identified talking about sensitive matters. While that is no guarantee they will be called, the odds increased this week after Libby's lawyer, Ted Wells, laid out a defense resting on the idea that his client, Vice President Dick Cheney's former chief of staff, had been made a "scapegoat" to protect Rove.

Editor & Publisher offers more details on Ari Fleischer as well:

As Fitzgerald's inquiry was heating up into who revealed CIA operative Valerie Plame's name to reporters, Fleischer stepped forward with an offer: Give me immunity from prosecution and I'll give you information that might help your case.

What prosecutors didn't know was that Fleischer was one of the leakers. And without immunity, he refused to talk. Not even a hint.

[..]I didn't want to give him immunity. I did so reluctantly," Fitzgerald said in court. "I was buying a pig in a poke."

Jeralyn does a little analysis of the developments