It took three voice votes, with supporters and opponents of the changes strongly expressing their preference, before a clearly flummoxed Los Angeles Mayor Antonio Villaraigosa declared himself satisfied that a two-thirds majority backed the new language, despite groans of displeasure from some delegates.

A senior Democratic source told CNN that Obama intervened to change the platform language, saying the president "didn't want there to be any confusion about his unshakeable commitment to the security of ... Israel." In addition, Democratic sources said Obama also asked aloud why the word "God" had been dropped.

"The platform is being amended to maintain consistency with the personal views expressed by the president and in the Democratic Party platform in 2008," said a statement by Wasserman Schultz, who heads the Democratic National Committee.

Struggle to define election

Both campaigns are fighting to define the election in the minds of voters. Republicans want it to be about Obama's presidency, while Democrats seek a choice between differing political ideologies on the size and role of government.

In particular, Republicans seek to shrink the size of government and end chronic federal deficits and rising national debt through reducing spending, reforming entitlement programs such as Social Security, Medicare and Medicaid, and slashing taxes on businesses and many individuals as a spur for economic growth.

Obama and Democrats argue that a deficit reduction plan also needs additional revenue, and they propose allowing tax rates on income of more than $250,000 for families and $200,000 for individuals to return to the higher levels of the 1990s.

Republicans oppose any kind of tax increase, and the impasse over that issue has been the main impediment to a comprehensive deficit reduction agreement during Obama's first term.

The race overall is very tight, with a new poll Tuesday showing Romney received little bounce from last week's convention intended to introduce him to voters just now turning their attention to the presidential race.

The CNN/ORC International Poll also indicates that less than 40% of registered voters said the GOP convention made them more likely to vote for Romney. At the same time, Romney got a slight bump in his favorable rating, and on being in touch with the middle class and women, although he still trails Obama on those two questions.