2004 Pathfinder SE Shudders while pressing a spongy brake petal

Pretty much sums it up. Initially driving, the brakes do not
progressively...brake in accordance to how much brake pressure I
want. It's either a "none or all" response and the car comes to a
dead halt and lurches if I press hard enough. After some time of
driving, the brakes are spongy and entirely unresponsive. The car has
20k miles on it...not to mention some kind of alignment/steering
problem that didn't go away after balancing and rotation. The
dealership claims bad tires, so I'm about to get some but I really
dont think the alignment/steering problem is wholly attributed to bad
tires. When I park and I leave the steering wheel perfectly straight
(by way of a level) left wheel is not straight and visibly out of
line.

Back on the brakes...at 20k miles...why are my brakes going? Does
warranty cover this? I believe I still have till the end of this year
because the car was purchased jan 2005.