There are two possible explanations for the pro-amnesty hysteria that occurred after the election.
1). Republican politicians who have always supported lax immigration policies saw an opportunity to pitch their unpopular immigration policies without risk of political blowback.
2). They may actually believe this stuff. After all, immigration policy debate in this country is primarily a mix of baby talk and mindless cliches (e.g. "nation of immigrants"), not intelligent dialog on the pros and cons of particular policy alternatives.