Words matter, Barack Obama has often said. They can even change the world. But rhetoric has not been enough to overcome the problems the president faces, and his challenge on Thursday night was to deliver another signature speech that was more than just a signature speech.

In many ways, Obama’s oratory has powered his political rise, but as he stands for reelection his reputation as a soaring speaker has become a hindrance — a skill that has brought Republican criticism that his eloquence far surpasses his policies and effectiveness as a politician.

Words can’t end the war in Afghanistan, fix a still-staggering economy or close a huge budget deficit, and Obama’s mission as he took the stage at the Time Warner Cable Arena was at its heart to provide an explanation for why a mixed first-term record argues for a second.

Striking the right balance on Thursday required all of Obama’s rhetorical dexterity as he delivered his second nomination acceptance speech — never an easy one for a president with a record to defend and a second term uncertain to happen.

His goal was to outline what that second term would look like and why more time would mean better results, while also reigniting the enthusiasm of the supporters who so animated his campaign four years ago.

As the Democratic National Convention entered its last hour, Obama strolled onto the royal-blue stage to a soundtrack of U2, smiling, taking in what will be his last national convention as a nominee.

“I know that campaigns can seem small and even silly,” he began. “Trivial things become big distractions. Serious issues become sound bites. And the truth gets buried under an avalanche of money and advertising.”

But he went on to raise the stakes, excite his base, even frighten it to a degree by defining, in clear words, what the Nov. 6 election is about.

The warning suggested the outlines of a second term, if not in specific policy proposals, in contrast to Republican proposals to repeal the nations’s new health-care law and cut taxes for the highest-income Americans.

“When you pick up that ballot to vote, you will face the clearest choice of any time in a generation,” Obama said. “Over the next few years, big decisions will be made in Washington — on jobs and the economy; taxes and deficits; energy and education; war and peace — decisions that will have a huge impact on our lives and our children’s lives for decades to come.”

Already highly anticipated, Obama’s speech came with an extra level of expectation at the end of what had been a rousing week for Democrats.

On the opening night of the convention Tuesday, first lady Michelle Obama was personal and emotional behind the lectern, reminding the delegates why they fell for her husband in the first place, just as she had years before. Former president Bill Clinton followed on Wednesday with a tour-de-force defense of Obama’s record and a comprehensive and cutting critique of his opponent.

By the time Obama appeared Thursday night, one of the most gifted orators of his generation faced the unlikely pressure of possibly delivering the third-best speech of the week. With his energy, clarity and at times partisan aggression, however, it was unlikely that most in the crowd would award him the bronze.

But Obama opted for a major speech that recalled familiar themes, offering little new, specific or surprising to a prime-time audience tuning in to the campaign perhaps for the first time in a serious way. At times, the address had the feel of a long compare-and-contrast list featuring himself and Republican rival Mitt Romney that harmed the speech’s coherence and sense of historic moment — and suggested that, as in the past few months, voters will be hearing various versions of it.

The address was one in a long line Obama delivered. There was his mesmerizing self-introduction in Boston at the 2004 convention — an outlandish honor for a hugely confident state senator who told friends that he would nail the speech, just as he did.

Just four years later, Obama, who had moved swiftly from the role of keynote speaker to subject of coronation, embraced the over-the-top grandeur of accepting the nomination amid a Greek colonnade arranged in the middle of a Denver football stadium.

His backdrop last time may have signaled democratic renewal — an appropriate setting for the “hope and change” he promised to bring to a partisan Washington and a worried country. Four years later, though, those remain two of the defining features of American life.

Obama delivered his last convention message before Lehman Brothers crashed, before the first bailout struggled to make its way through an already bitter Congress, and before a presidential transition during which advisers warned him that the economy he had inherited was in far worse shape than expected.

On a frigid January day on the Mall, Obama delivered a grave inaugural address, whose warnings of even more difficult days ahead may have been ignored by the freezing thousands thrilling to the fact that the nation’s first African American president was taking the oath of office.

On Thursday, he reminded the audience of how much work remains. “I won’t pretend the path I’m offering is quick or easy,” Obama said. “I never have. You didn’t elect me to tell you what you wanted to hear. You elected me to tell you the truth. And the truth is, it will take more than a few years for us to solve challenges that have built up over decades.”

The inheritance and the halting recovery — the country he took over, the country as it is now — have been spun through his recent stump speeches to make the point that, although progress has been made slowly and not always steadily, more must be done.

In his telling of the story, as he did Thursday, Obama is the one to do it. But his mission here was ar more complicated than a look-back-in-anger approach he has used in Colorado, Iowa, Ohio and other swing states.

Some of it involved showcasing his record — fulfilling his pledge to end the war in Iraq, pushing through health-care legislation that proved politically costly but achieved something presidents for more than a century could not. He is drawing down troops from Afghanistan after an early-term escalation — the United States’ longest war and one that Romney did not mention in his nomination acceptance speech last week.

Obama criticized his rival’s recent comments on foreign policy, giving the remarks at times the feel of a stump speech voters will be hearing. He noted that Romney said “it was ‘tragic’ to end the war in Iraq, and he won’t tell us how he’ll end the war in Afghanistan.”

“I have, and I will,” Obama said.

He said, “My opponent and his running mate are new to foreign policy, but from all that we’ve seen and heard, they want to take us back to an era of blustering and blundering that cost America so dearly.”

He added: “After all, you don’t call Russia our number one enemy — and not al-Qaeda — unless you’re still stuck in a Cold War time warp.”

Obama had originally planned to give his speech at nearby Bank of America Stadium, a more dramatic setting with a far larger capacity than the indoor arena. Campaign officials said forecasts for severe weather were the reason for the change, but Republicans questioned whether the real reason wasn’t that Obama couldn’t fill the outdoor venue.

Obama’s message was directed largely at those outside the arena, the swing-state undecideds that comprise about 7 percent of the electorate.

He also addressed those constituencies — women, Latinos, African Americans, gays and others — who strongly support his candidacy. Maximizing the turnout of these voters is key to Obama’s success in several swing states, partly to make up for a decline in support from white men, independents and others.

“On every issue, the choice you face won’t be just between two candidates or two parties,” Obama said. “It will be a choice between two different paths for America.”