Was illegal immigration non-enforcement ever challenged under "equal protection" theory? Did it affect illegal immigration related legislation?

Question

1. Illegal immigration is either a misdemeanor or a felony in USA (depends on specifics of what an individual did).

2. 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.

3. 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).

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As such:

1. 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?

2. 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?

Answer 1

As far as my research has been able to determine, there has never been a challenge to immigration enforcement based on equal protection. The logic for this is fairly simple - such a challenge would require the showing of unequal enforcement, not lack of enforcement. Prosecutorial Discretion is a well-established principle of the legal system, and has been shown to be allowable many times.

The term prosecutorial discretion is commonly used to describe the wide latitude that prosecutors have in determining when, whom, how, and even whether to prosecute apparent violations of the law.

It would appear that there have been no substantial challenges on other grounds either.

The Congressional Research Service paper Discretion in Immigration Enforcement: legal Issues looked into the issue at length. Part of the summary reads:

Particular exercises of discretion could potentially be checked by the Constitution, statute, or agency directives. Selective prosecution, or prosecution based on race, religion, or the exercise of constitutional rights, is prohibited, although aliens generally cannot assert selective prosecution as a defense to removal. A policy of non-enforcement that amounts to an abdication of an agency’s statutory responsibilities could potentially be said to violate the Take Care Clause. However, standing to challenge alleged violations of the Take Care Clause may be limited, and no court appears to have invalidated a policy of non-enforcement founded upon prosecutorial discretion on the grounds that the policy violated the Take Care Clause.