I've got some bad news for you, there's a bill being debated in Canada about giving US officials the discretion to hold or detain travellers at pre-clearance centres:

http://www.cbc.ca/news/politics/pre-clearance-border-canada-...

https://openparliament.ca/bills/42-1/C-23/

If it passes in Canada, it's only a matter of time before it happens in Ireland (or you lose the pre-clearance option).