Trump touts dubious research in border wall tweet

Sources:  @realDonaldTrump (highlight added); Southern Poverty Law Center

Economic Policy Institute FAQ (excerpts)

9. Do unauthorized immigrants increase budget costs for states or the federal government?

Unauthorized immigrants are a net positive for public budgets because they contribute more to the system than they take out.16 Unauthorized immigrants generally cannot receive benefits from government programs, except in some cases, such as when unauthorized immigrant children receive public education, and in some states that allow unauthorized immigrants to attend state colleges at in-state tuition rates. Nevertheless, most of these unauthorized immigrants will still pay taxes. 

Unauthorized immigrants are also unlikely to receive any income credits available through the tax code, or to receive a tax refund if they overpaid in their regular payroll withholdings.