There are over 2000 domestic flights in the US daily.
For a single air marshal per flight that would require (considering that air marshalls don't work 24 hours a day and you can't always get directly from one flight to another) around twenty thousand air marshals.
And it's just as easy to hijack a plane outbound for a foreign country as it is a domestic flight.
When you add in overseas flights, the number goes up to 5000 per day, and the number of air marshals needed goes up to around fifty thousand.
If you consider an average salary of $50,000, that's 2.5 billion dollars just in salary, not to mention pension, medical, training, administrative overhead, supervision, transport and many other financial costs. The rough estimate for government is that each person on the payroll costs three times as much as his salary. That makes a conservative estimate of 7.5 billion.
To have your scenario of two on each flight, double all of those numbers with a grand total of 15 billion.
The total budget for the US Dept. of Homeland Security is only 40 billion. That means that two air marshals on each flight would take up over a third of the entire DHS budget. I don't think so.
It's not possible to have even a single air marshal on every flight, much less two.
The reality is that about 5% of all domestic flights carry an air marshal.
Speaking of "Homeland Security", I'll bet a lot less than that carry an armed pilot - and this is over three years after 9/11.
In WWII and with this time frame, we would be at the Rhine in the heart of Germany!