There are about 9m bikes registered in the US. Some of them of course are owned by people with more than one. The number of active riders in the US is somewhere between 6-7 million. Really think 1 in 3 or 4 has time to ride to DC for this? Neither do I.Adding 2 million bikers? Hell, even adding a thousand is going to be crazy.
Nobody thinks 2 million will show up. The Muslim guy say "million person" so they say two. Neither is likely to break the "thousands" mark and everybody knows it.