"potentially disabling the vehicle or person" How euphemistic ! Like "terminating with extreme prejudice" BTW, didn't I see this in a movie with Ahhnold?

I considered the idea years ago but decided that once you have a laser capable of generating the plasma trail the electrical discharge would be superfluous.
The laser could also be useful as an active lightning rod system whether or not you can use the super surge of electricity.

don't use this in a thunderstorm.... :P

Don't get it. If you have enough energy to fire a laser beam... why don't you just use the laser beam to destroy whatever target you want to destroy... since it's a 50 billion watt laser, I'm pretty sure it's stronger than a jolt of electricity, even if it only lasts 2 trillionths of a second. In fact, this is probably better, because this can be targeted accurately (say at the engine of an enemy tank 100 km away) and nobody will be able to see it. The target would just explode seemingly spontaneously. common sense, anybody?

@Daniel Socrates Tan
One thing you need to know about tactical lasers, is that they aren't instantaneous. It takes a good twenty seconds of exposure to burn a hole in a missile or vehicle. And that still doesn't guarantee that it will explode. Plus, the point of this weapon is to be tunable to different targets and sometimes 'NOT' to fry them on purpose.

For those asking the question why not just use the laser to do the damage... Most of you are leaving off the most important measure of the laser pulse: "two-trillionths of a second" That is Two picoseconds. If you hit a soft target like a person with that you might reasonable be ale to do some harm but it would only be skin deep (better hope you hit him in the eyes). A hard target like a vehicle wouldn't even notice it. You would need to be able to maintain the beam for almost a full second to do significant damage to a vehicle especially an armored vehicle. Electricity on the other hand can destroy electronics, and nerve pathways with a very brief pulse.
So in short the laser pulse duration is too brief to do damage, current laser technology would vaporize itself before delivering that kind of power for a usefull timespan, and electricity can do much more damage.

Slowburn, are you a defense contractor? Since you are always on top of all the new defense technologies, maybe you should be getting paid for it.
Also, the laser must not last long enough to do any real damage, or else they would not have even considered using it in this manner. 50 billion watts is a hell of a lot to keep going. The electricity jolt could be controlled enough that it can knock a person out, disable a vehicle, or detonate an explosive device. You don't even have to aim it perfectly to hit a huge tank with it, just be near enough that it takes the path of least resistance.

Why not deliver a charge sufficiently disruptive to the very structure (or parts of) the object to be "affected"?

@Daniel Socrates Tan
C'mon, everyone knows that laser beams are blue, unless you're the bad guy, then they're red...

The problem is how are you going to put the steel ground plates under the target?
Next a laser heats the air, not generatoe an electromagnetic field.
Electricity does take the path least resistance but that isn't nessasarily the target. It might just as well be the shooting vehicle, humid air, etc.