Book #2 in the Star Trek: Destiny trilogy.
"On Earth, Federation President Nanietta Bacco gathers allies and adversaries to form a desperate last line of defense against an impending Borg invasion. In deep space, Captain Jean-Luc Picard and Captain Ezri Dax join together to cut off the Collective's route to the Alpha Quadrant."
One of those backing Bacco is the Cardassian ambassador Elim Garak.