This is the TSA, expecting an exact answer is wishful thinking. The procedure is pretty much whatever the screeners decide it is on that day; it varies from airport to airport, from checkpoint to checkpoint, even from hour to hour.

You cannot be arrested for failing to complete screening, since it is not a crime but a violation of an administrative search (ie.civil offence), punishable by an $11000 fine. If a LEO is summoned he/she can detain you while the screeners record your information, the screeners themselves cannot legally detain you but will do so simply by refusing to return your belongings. If you try to retrieve them forcibly they will no doubt cry 'assault'. All that said, I don't know if anyone has actually been fined.

Corrections ?