As Lindsey Graham and his fellow Republicans explain it, their sudden turn against conferring citizenship on anyone born in the United States was prompted by the mortal threat of "anchor babies" -- the children of foreigners who scurry to the States just in time to give birth to U.S. citizens.

The Republican war on the 14th Amendment's citizenship clause is indeed directed at a mortal threat -- but not to the American nation. It is the threat that Latino voting poses to the Republican Party.

By proposing to revoke the citizenship of the estimated 4 million U.S.-born children of undocumented immigrants -- and, presumably, the children's children and so on down the line -- Republicans are calling for more than the creation of a permanent noncitizen caste. They are endeavoring to solve what is probably their most crippling long-term political dilemma: the racial diversification of the electorate. Not to put too fine a point on it, they are trying to preserve their political prospects as a white folks' party in an increasingly multicolored land.

Absent a constitutional change -- to a lesser degree, even with it -- those prospects look mighty bleak. The demographic base of the Republican Party, as Ruy Teixeira demonstrates in a paper released by the Center for American Progress this summer, is shrinking as a share of the nation and the electorate. As the nation grows more racially and religiously diverse, Teixeira shows, its percentage of white Christians will decline to just 35 percent of the population by 2040.

The group that's growing fastest, of course, is Latinos. "Their numbers will triple to 133 million by 2050 from 47 million today," Teixeira writes, "while the number of non-Hispanic whites will remain essentially flat." Moreover, Latinos increasingly trend Democratic -- in a Gallup poll this year, 53 percent self-identified as Democrats; just 21 percent called themselves Republican.

To be sure, the wretched state of the economy could drive some otherwise Democratic-inclined Latino voters to the GOP this November. But Republicans are doing their damnedest to keep this from happening. Their embrace of Arizona's Suspicious-Looking-Latinos law and their enthusiasm for stripping Latino children of their citizenship will only hasten Latinos' flight.

Sentient Republican strategists such as Karl Rove have long understood that unless their party could win more Latino votes, it would eventually go the way of the Whigs. That's the main reason George W. Bush tried to persuade congressional Republicans to support immigration reform. But most lawmakers, reflecting the nativism of the Republican base, would have none of it.

By pushing for repeal of the 14th Amendment's citizenship clause, the GOP appears to have concluded: If you can't win them over -- indeed, if you're doing everything in your power to make their lives miserable -- revoke their citizenship.

On this page last week, my colleague E.J. Dionne Jr. rightly noted that by attacking the amendment, Republicans seek to undo one of their party's greatest and most inclusionary achievements. Civil War- and Reconstruction-era Republicans took pains to ensure the citizenship not only of freed slaves and their children. They -- in particular, Abraham Lincoln -- also decided not to permanently keep millions of Confederate soldiers and sympathizers from regaining their citizenship.

The Confederates had renounced all allegiance to the United States. They made war on the United States -- the Constitution's definition of treason -- and, in an effort to keep 4 million Americans enslaved, killed more of our soldiers than any foreign army ever did.

Yet Lincoln was determined to make it easy for Confederates to regain their citizenship. By taking an oath to support the United States and its Constitution, Confederates were made Americans again.

Suppose, though, that Lincoln had been filled with the spirit of today's Republicans. The crimes that Republicans ascribe to today's illegal immigrants pale next to those of Confederate leaders and supporters (chiefly, treason). A Lindsey Graham-like Lincoln would never have let the Confederates regain citizenship. Moreover, he would have denied citizenship to their children and their children's children. A large share of the nation, certainly of the white South, would have drifted endlessly in a legal limbo. The current Republican Party, anchored as it is in the white South, would scarcely exist.

So, the question for Lindsey Graham is: Are you serious about revoking the citizenship of 4 million children, their children and their children's children? How about a package deal: Stripping their citizenship in return for stripping the citizenship of Confederate descendants. A sort of Missouri Compromise for our times. Bipartisanship in action.

Senator, let me know what you think.

meyersonh@washpost.com