Lone Republican stops bill in Senate

Somebody needs to fill me in on Senate procedures. Tell me, how is it that a lone Republican can block a Democratic bill in the Senate today, when lots of Democrats couldn't block anything the Republicans did before the change of hands?

From TPM Muckraker:

Democrats had sought to push through a bill today that would restore the law on U.S. Attorneys back to its earlier form, before a change was slipped into the USA PATRIOT Improvement and Reauthorization Act last year. That change effectively allowed the administration to permanently appoint U.S. Attorneys without Senate confirmation. The bill would set a 120 day deadline to those appointments, when a federal judge would appoint a permanent replacement if the president hadn't nominated one for the Senate to confirm -- which is the way the law was for twenty years before last year's change.

But the bill was blocked by Sen. Jon Kyl (R-AZ), who, along with the administration, argues that having judges appoint federal proscutors raises separation of powers issues.