Let us say Italy decides to pull out of EU and screws up the Euro. US banks have invested in hidden currency SWAPS and disclose to Fed gov that they took heavy losses and unable to payoff their margin calls. Wall Street bankers inform the Fed and US Treasury that if they do not get a bailout they will implode the US financial system. Within 72 hrs the US system collapses, Fed gov calls a bank holiday (banks close). ATM machines freeze, credit card freeze and worst food stamp cards freeze and unemployment checks bounce. Inner cities erupt into welfare riots, and your LEO will be more then willing to shoot the rioters. Homeland Security will go into action with their 2700 MRAPs, NG will be mobilized and LEO will fall in line as soon as Fed troops and DHS arrives to put down the riots. All this power and capacity being stockpiled not for just for Obama, it is for the next POTUS, so the gov is ready when the banks finally fall apart and the gov cannot issue entitlement checks anymore.
It is not an established tradition for US LEOs to bravely catch bullets just so a few homeless people in another street can be saved. When riots begin the law enforcement ends. The timeline of LA riots (1992) shows that the police fled the streets. The Koreans were holding the fort because 911 did not answer, not because they wanted to get a few murders under their belts. Wikipedia offers this quote:
"I want to make it clear that we didn't open fire first. At that time, four police cars were there. Somebody started to shoot at us. The LAPD ran away in half a second. I never saw such a fast escape. I was pretty disappointed."
The riots of 1992 were put down by the National Guard, without use of force. Wikipedia does not mention the police as a major peacemaker. Police is not an army, and a supervisor cannot send a police officer to death because it is strategically advantageous. If one shooter is holed up somewhere, the police needs 100 officers and air support because they are very safe operators. If mass riots are in progress, the police simply doesn't have enough officers to achieve such an overwhelming force. Individual officers will not survive in a riot. That's why they are not a player. They are not trained, not conditioned, and not expected to die for their country. They can maintain law and order only when the local majority supports them.
If the riots are calming down, the police will be cautiously making their appearance, "supporting" the troops. Riots will be calming down if they have a finite cause, like a beating of one guy, or a hurricane, or an earthquake. Riots will not be calming down if the trigger situation remains active. The crash of US financial system is not something you can repair overnight. This means the riots will not be that easy to stop, and the police will be exactly where I'd expect them to be - with their families, and hopefully with their neighbors, taking part in the mutual defense.
Those MRAPs will not be a wunderwaffe either. They are resistant to IED, but they are not resistant to anti-tank weapons; they cannot pass over trenches or barricades; they can be buried under demolished buildings. They don't seem to have effective weapons that can be operated from the inside; they only have gun ports for small arms. They appear to be very vulnerable to incendiary weapons - they have too many crevices, and the rubber of the tires is certainly going to burn. The vehicle has neither the efficient (carbon) filters nor the positive air pressure inside - this makes the passengers dependent on clean ambient air, which is in short supply if there are fires all around (especially if it's their own MRAP that is burning.)
In essence, this MRAP is only usable for delivery of troops. Once they are there, they have to disembark and become vulnerable on their own. It is not a fighting vehicle like a tank; it has no integrated weapons. It's just an armored carrier.