Illegal immigration is either a misdemeanor or a felony in USA (depends on specifics of what an individual did).
Under ordinary circumstances, if a resident would commit a felony or even a misdemeanor (petty theft, prostitution, drunk&disorderly) they are more likely than not going to be arrested, and most assuredly prosecuted.
Despite that, illegal immigrants are very rarely arrested and prosecuted even when LEOs know who/where they are (e.g., a guest of Administration during President's speech; during a pro-illegal-immigration rallies).
Was there ever a legal challenge (either against non-illegal-immigration arrest/prosecution; OR against lack of illegal-immigration-related ones) that was specifically based around "equal protection under the law" clause of the Constitution? If so, what is the current status of such a challenge as far as how valid the legal theory is?
Based on #1, do any of the illegal immigration related bills in US Congress take into account the possibility of (or current status of if #1 answer is "yes") such challenges?