"Key word being "federal" so it must be an American brand. Ford, GM or Chrysler. Not all vehicles are good for all things..."
It may be poetic license and I'm not familiar with federal purchasing policies, but in the TV show Bones agent Booth drives a Toyota SUV, so on that issue you may not necessarily be confined to American vehicles.
I live near a retired patrol deputy and he said the Taurus, while a nice enough car, is not really practical for patrol duties as the back seat is too cramped for prisoners after the cage is installed, and there's not enough overall room (front seat area and trunk) for all the gear a modern police officer is required to carry, especially in a 2-person unit. However, as prisoner transport appears to be a relatively minor aspect of the OP's story, this may not matter so much.
The OP indicated her fictional federal agency needs a vehicle that's fast and tough. To me that screams for an SUV. The Jeep Grand Cherokee, for example, is available in an SRT version with almost 500 horsepower (quarter mile just over 12 seconds flat - I've seen them at the local drag strip). With modern multi-speed transmissions (Fiat/Chrysler makes a 9 speed and Ford is introducing a 10 speed), even a 5,000 or 6,000 pound SUV with 450-500 horsepower can pick 'em up and put 'em down pretty well; no match for a Dodge Hellcat for sure, but well enough to keep in contact with most street cars. As for handling, with the influence of computers and sophisticated programming, even SUVs will handle surprisingly well (again, not Ferrari class, but much better than you'd expect). These include 4 wheel anti-skid technology (the computer senses when you're about to skid in a turn and applies the appropriate brake independently to mitigate the skid) and computer controlled shock absorbers.
As for toughness, you just can't beat a purpose made SUV (heavy frame and suspension).
Otherwise, a number of posters have hit on possibly the best solution: federal, state and local jurisdictions have property seizure laws (unconstitutional as far as I'm concerned, but I wasn't asked), so all police agencies have access to all types of cars, trucks, vans, big rigs, boats, etc.