Mitt Romney's faith emerged as little more than a subordinate issue on the US campaign trail but, with the Republican nomination now securely in his grip, are American voters ready for a Mormon president?

The candidate made history late on Tuesday when he became the first of his faith to win the nomination of a major political party. The achievement illustrates how far the acceptance of Mormons has come since the church was founded in the US nearly two centuries ago.

A President Romney could be a golden opportunity for a church aiming to broaden its base across the US and internationally, but it is also fraught with risk.

Romney, who outlasted several rivals in a bruising primary battle, has become the unlikely flag-bearer of a Republican movement heavily influenced by evangelical Christians, some of whom have called Mormonism a "cult".

But despite persistent scepticism about the faith - a Bloomberg News poll in March showed that more than one in three Americans hold an unfavourable view of the Mormon church - associate professor Brandon Rottinghaus, of the University of Houston, said on Wednesday that he thinks Americans are ready for a Mormon president.

"There will be a small segment of evangelical voters who won't accept the Mormon faith as a tenet of Christianity, but most voters will be tolerant," Rottinghaus said.

"The big challenge for the Romney campaigners was to get through the Republican primary process without a religious uproar, a task they have completed."

The Church of Jesus Christ of Latter-day Saints has remained silent on the presidential campaign, even though Romney's milestone could be seen as a plus for Mormonism.

"The church's political neutrality is well established and we have no interest in providing commentary on a political race," said Eric Hawkins, a spokesman for the Utah-based church.

The breakthrough is tempered by the historic nature of the 2008 race, which achieved several firsts: Americans elected Democrat Barack Obama as their first black president, Sarah Palin became the first female Republican vice-presidential pick, and Hillary Clinton almost earned her party's nomination.

And in 2000, Democrat Al Gore very nearly won the White House with Joe Lieberman, an orthodox Jew, as his running mate.

"Primary audiences in both parties are used to seeing diversity among the pool of potential nominees," Rottinghaus said.

Romney is not the first Mormon to try for the White House. Church founder Joseph Smith ran in 1844, in part to press for greater civil liberties for members of his nascent church.

With the general election now in full swing, Obama and Romney are hammering each other over economic policy.

But character and personal background form a piece of the puzzle and Romney's faith is likely to come under scrutiny.

There are 6million Mormons in the US and three out of four describe themselves as conservative.