First Lady Michelle Obama has made an impassioned speech backing her husband, President Barack Obama, for another four-year White House term.

Closing the first night of the Democratic convention in North Carolina, Michelle Obama spoke of the couple’s shared background in struggling families.

She said it was “extraordinary privilege” to serve as first lady.

President Barack Obama will formally accept the nomination on Thursday, and face Republican Mitt Romney in November.

A recent opinion poll shows Michelle Obama maintains a thin lead over Mitt Romney.

But an ABC News/Washington Post poll released as the convention got under way in Charlotte, North Carolina, showed Barack Obama with the lowest pre-convention favorability for an incumbent president since the 1980s.

The president is aiming to recapture the political spotlight over the next few days, after last week’s Republican convention.

Michelle Obama said that four years ago she “believed deeply” in her husband’s “vision for this country” but worried about how a run for president would change their life and the life of their daughters.

In a speech roundly welcomed by a hyped-up crowd, she shared memories from their 23-year relationship, and noted that she had found a “kindred spirit” in a man whose values were similar to hers.

“Barack and I were both raised by families who didn’t have much in the way of money or material possessions but who had given us something far more valuable – their unconditional love, their unflinching sacrifice, and the chance to go places they had never imagined for themselves.”

The first lady’s speech connected their shared background to the values she said guided Barack Obama as president.

“As president, you can get all kinds of advice from all kinds of people,” she said.

“But at the end of the day, when it comes time to make that decision, as president, all you have to guide you are your values and your vision and the life experiences that make you who you are.”

She said Barack Obama was inspired by his own background when advocating for laws involving fair pay for women, healthcare and student debt.

He had not been changed by the White House, she said, and was “still the same man I fell in love with all those years ago”.

“He’s the same man who started his career by turning down high-paying jobs and instead working in struggling neighborhoods where a steel plant had shut down, fighting to rebuild those communities.”

In the toughest moments, Michelle Obama added, “he just keeps getting up and moving forward… with patience and wisdom, and courage and grace.”

Earlier, the chair of the Democratic National Committee, Debbie Wasserman Schultz, brought the gala into session with a strike of the gavel at 17:00 EDT.

Shortly after the convention opened, delegates cheered their backing for the party’s new platform in a open voice vote.

Among the changes found in the text of the party’s 2012 platform was the removal of language from the Middle East section referring to Jerusalem as the capital of Israel.

That message was replaced with a passage referring to the party’s “unshakeable commitment to Israel’s security” and Barack Obama’s “steadfast opposition to any attempt to delegitimize Israel”.

The change prompted criticism from Republicans and Mitt Romney, who accuse Barack Obama of “selling out” a key US ally.

Tuesday’s first session saw a series of Democratic governors, members of Congress, mayors and electoral candidates speak in support of Barack Obama and his policies, most notably his much-criticized healthcare reform law.

A video tribute to the late Senator Edward Kennedy included clips from his 1994 Senate debate with Mitt Romney, and independent Rhode Island Governor Lincoln Chafee argued that his former party – the Republicans – had lost their way and had forfeited the label of conservative.

Former White House Chief of Staff Rahm Emanuel said the next president would set the tone for the next 40 years.

“It will be the president’s leadership that determines how we as a nation meet the challenges that face the middle class. It is the president’s values that shape a future in which the middle class has hope,” he said.

Julian Castro, the Latino Mayor of San Antonio, Texas, gave the keynote address immediately before Michelle Obama.

The Democratic gathering will see Barack Obama and Vice-President Joe Biden formally re-nominated as the party’s presidential and vice-presidential candidates on Wednesday.

Later that evening, there will be speeches from Elizabeth Warren, who is fighting Republican incumbent Scott Brown in a high-profile race for a Massachusetts Senate seat, and former President Bill Clinton.

The convention culminates on Thursday with speeches from Barack Obama and Joe Biden.

Republican nominee Mitt Romney is expected to spend the week preparing for a series of debates with Barack Obama.

The gala also offers the Democrats the chance to make a high-profile pitch to voters in North Carolina, a state that narrowly voted for Barack Obama in 2008, but is now firmly up for grabs.

As they did four years ago, the Democrats will take the event outside the convention centre for the president’s prime-time speech, taking over a 74,000-seater stadium in Charlotte for the final night of speeches – despite a poor weather forecast.

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