Rupert Cornwell: Are you now, or have you ever been, a migrant?

Out of America: If you believe the hysteria, foreign women are queuing up to give birth to automatic US citizens

(getty images)

To state the blindingly obvious, it matters where you were born. Back in the distant days when Yorkshire ruled English cricket, only native Tykes were entitled to play for the county. Many were the tales of Yorkshiremen in exile marching their pregnant womenfolk back to the promised land in tones that brooked no contradiction: "Thah'll whelp this 'un in Yorkshire, lass."

If you believe America's anti-immigrant lobby, something similar is going on here. But there are two important differences. First, of course, San Diego and El Paso, not Doncaster and Barnsley, represent the promised land. And second, those seeking to have children born in the US are not homesick Americans. They are people who have no legal right to live here in the first place.

Hence the unlovely term of "drop and leave". It refers to those illegal immigrants seeking to have a so-called "anchor baby" who is automatically an American citizen by dint of having been born on American soil, just as those Yorkshire newborns were qualified by birth to play cricket for the county. These babies are supposed to "anchor" their foreign parents to the US, making it less likely they will be deported for immigration offences.

Just how widespread is "drop and leave" is a matter of much dispute. The anti-immigration lobby would have you believe it is a threat to national security. Others argue that such claims have as much connection to reality as those tales of Yorkshire past, noting for good measure that under US law, no citizen under 21 can apply to sponsor his or her foreign parents for residency. But as with love and war, all is fair in the ever more emotional immigration debate here.

In April, Arizona passed legislation (now blocked in part by federal courts) that would have required police to conduct spot checks if they had "reasonable ground" to suspect a person might be in the country illegally. Last week, Florida proposed what could be an even tougher law. Immigrants would face up to 20 days in prison if they were caught not carrying valid documents, while judges could pass stiffer sentences on illegal immigrants convicted of the same crimes as legal residents.

But for some immigration "reductionists", as they are charmingly known, even these measures are not enough. America must eliminate "anchor babies" – and that means tackling the root of the problem, the constitutional amendment that guarantees citizenship to almost everyone born in the US. The 14th amendment was passed in 1868, three years after the American civil war, to ensure that blacks were citizens on an equal footing with whites. "All persons born or naturalized in the United States, and subject to the jurisdiction thereof," it says, "are citizens of the United States." The bit about "jurisdiction" is generally held to exclude children born to foreign leaders here, or foreign diplomats serving in the US. Various efforts have been made to exclude the children of all foreign nationals, but every one has failed.

The amendment, incidentally, scotches the arguments of so-called "birthers" about Barack Obama's qualification to be president. That Ann Dunham, his mother, was only 18 when he was born in 1961, and that his father was a native Kenyan and a British subject, are irrelevant. The future president was born in Hawaii, a state of the union since 1959. End of story. And even the stricter 14th amendment sought by critics would have made no difference. One of Obama's parents was an American.

Nonetheless, the campaign for a more tightly framed amendment has attracted notable supporters. Lindsey Graham, the South Carolina senator who in the past has been a rare Republican willing to work with Democrats, has changed his tune. He now promises to work to remove the constitutional right of "birthright citizenship" for children born in the US to immigrants.

John McCain, the Republicans' presidential nominee in 2008, is another. McCain once advocated sweeping reform that would allow illegal immigrants a path to legal residency and citizenship. But he, too, is taking a harder line – one not unconnected with his spirited right-wing challenger in next week's primary for the Arizona Senate seat McCain has held since 1987. Last year 92 House members also signed a resolution demanding a change to the 14th amendment.

But their chances of success are slim. Amendments to the US constitution are fiendishly difficult to secure. In the entire history of the republic, only 27 amendments have been enacted, and of those the first 10 were a single batch in 1791, and collectively form the Bill of Rights.

In recent years, proposed amendments to ban gay marriage and flag burning have popped up repeatedly. Neither has made it out of Congress. "Birthright citizenship" is likely to meet a similar fate. Indeed, a poll last week found that a slim majority of voters opposes tinkering with the 14th amendment. Like Yorkshiremen, Americans may be suspicious of foreigners in their midst. But, like Yorkshiremen, they don't like to be rushed.