Most liberals and many economic conservatives argued that support for such legislation was a political imperative for Republicans. Otherwise, they would continue to lose Hispanic voters, an inevitably increasing segment of the electorate, by 2-1 margins.
That argument was bolstered by the 2004 exit poll, which showed comprehensive immigration supporter George W. Bush getting 44 percent of the Hispanic vote. That percentage may have been inflated, but if Bush had received the percentages of John McCain (31) or Mitt Romney (27), he would probably not have been re-elected.
Republican opponents of comprehensive immigration respond that granting citizenship to illegals would enfranchise millions of Hispanics who would vote heavily Democratic on economic issues.
And they argued that a nation based on the rule of law should not reward lawbreakers. On that basis most Republicans voted against the comprehensive bill co-sponsored by Chuck Schumer and Marco Rubio that passed the Senate in June 2013.
Meanwhile, as the politicians debated, the facts on the ground changed. Net migration from Mexico, the source of more than one-third of all immigrants and about 60 percent of illegals from 1982 to 2007, fell to zero after that.
And polls showed that most Americans favored legalization of the so-called Dreamers, young adults whose parents had brought them illegally across the border when they were children.
Barack Obama, who didn't push immigration legislation when Democrats had Congressional supermajorities in 2009-10, announced he would no longer deport Dreamers who met certain conditions. As on many other issues, he was not troubled by the fact that the Constitution gives the task of passing laws to Congress and requires the president only to faithfully execute them.
That didn't seem to have any political downside. But the facts on the ground changed again. According to the Obama administration, only 4,000 unaccompanied minors approached the border in fiscal year 2011. That rose to 21,000 in fiscal year 2013 and to 47,000 in fiscal year 2014.
Almost all seem to have come overland through Mexico from the Central American republics of Guatemala, Honduras and El Salvador. Reports of this unanticipated surge have been filling television screens.