Immigration: The mother of all issues

"Amnesty" may have been his undoing.

The 2013 "Gang of Eight" immigration deal arguably killed Marco Rubio's presidential run.

"Build the wall," is Donald Trump's sole consistent policy — besides his proposed moratorium on Muslim immigration.

How did immigration become the dominant issue in the Republican primary?

It's a question that's baffled Republican elites and Beltway conservatives who were caught off guard by the issue's salience. While Washington politicians debated child tax-credits, Obamacare replacements and ethanol mandates, Trump went out and called for a wall to keep out the rapists that Mexico was supposedly sending north.

If immigration sank Rubio, it wasn't because voters agreed with Trump's policies — exit polls actually show most Republican primary voters favoring Rubio's approach to illegal immigrants, which includes a path to legalization.

Instead, the issue was seen in a much rougher sketch by voters: Rubio tried to cut a deal for amnesty; Trump wants to keep out the illegals.

Immigration matters so much first, because it touches on all important policy areas.