The Protestant Irish (actually a mixture of Scots, Irish and Huguenot refugees from the Continent stated arriving in the late 1690's following the St. Bartholomew's Massacre's.
The failure of the Potato crops in the 1840's started massive Irish Catholic immigration. As they worked cheap, the powers that be welcomed them with warm arms.
BUT, some of these Irish lads went into the US Army (no draft in those days) and went on to serve in our war with Mexico.
While there, a number of Mexican Catholic priests were allowed to cross the lines for spiritual guidance of the lads.
However, these Priests convinced these subjects to disobey the oath they had willingly taken to serve 'faithfully in US forces", and then they switched sides.
They choose to fight for the dictator Santa Ana, against their former comrades in arms, that being the US Army.
Remember, these were not draftees yanked fresh off the boats, but men who enlisted for the pay and honors....
The backlash from this betrayal, was even greater than 9-11.
Other Irish Catholics really tried to make up for the betrayal by their coreligionists - by faithful and honest service, but the damage was done. (See NY 69th Infantry)
Today these betrayers are honored in Mexico as the "San Patrico Battalion.
Wouldn't be surprised to the Bushes laying Wreaths at the various monuments in Mexico that honor them. Really wouldn't.
Americans are deluded by the myth of the easy assimilation of immigrants. In reality it took 100 years to assimilate the Irish. Evidently some have assimilated into minority grievance just like most of my coreligionists.