[PHILADELPHIA] US President Barack Obama will spearhead a Democratic effort to paint Donald Trump as unfit to be commander-in-chief Wednesday, contrasting the Republican nominee with his vastly more experienced rival Hillary Clinton.
Mr Obama, acting as a character reference for his former primary foe and secretary of state, will make the case to Democrats gathered in Philadelphia for their national convention that Mrs Clinton is uniquely qualified to be president.
"Nothing truly prepares you for the demands of the Oval Office," the two-term president will say, according to excerpts of his speech released by the White House.
"Until you've sat at that desk, you don't know what it's like to manage a global crisis or send young people to war," he will say. "But Hillary's been in the room; she's been part of those decisions." "I can say with confidence there has never been a man or a woman more qualified than Hillary Clinton to serve as President of the United States of America."
Having fought his own angst-ridden primary against Mrs Clinton eight years ago, Mr Obama could offer a potent testimony about how a rival became an ally and evenhanded advisor.
For four years, Mrs Clinton traveled the globe pushing Mr Obama's foreign policies as America's top diplomat.
The White House would like to make November's crunch election a battle about competence versus incompetence, steady versus capricious, knowledge versus entertainment.
On Wednesday, Mr Obama will be one of a string of Democratic national security heavyweights - from former CIA director Leon Panetta to Vice-President Joe Biden - who will appear before the convention to explicitly and implicitly question Mr Trump's temperament.
In an incendiary press conference, Mr Trump launched a pre-emptive attack against Mr Obama, calling him "the most ignorant president in our history."
Democrats will hope to capitalise on a string of perceived foreign policy missteps, culminating in Mr Trump's suggestion that Russia spy on his rival Mrs Clinton.
The Republican nominee caused howls of outrage on Wednesday, with a reference to thousands of Clinton emails held on a private server that were deleted.
"Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing." Mr Trump said.
Mrs Clinton says the mails were personal and not work-related, but for Republicans, it is a smoking gun for a cover-up involving her use of a private server during her time at the State Department.
The FBI concluded this month that Mrs Clinton had been "extremely careless" in her handling of classified material via a private email server, but did not recommend that she face criminal charges.
"This has to be the first time that a major presidential candidate has actively encouraged a foreign power to conduct espionage against his political opponent," said Mrs Clinton's top foreign policy aide Jake Sullivan.
"This has gone from being a matter of curiosity, and a matter of politics, to being a national security issue."
Mrs Clinton on Tuesday became the first woman to win the presidential nomination of a major US political party, teeing up the November showdown with Trump.
Democrats had "put the biggest crack" yet in the glass ceiling for women, she said in a video message to the convention.
In the twilight of his second term, Mr Obama faces ever-dwindling opportunities to address the nation, mold his legacy and influence the 2016 race.
But on Wednesday, he has a prime-time chance when he appears before thousands of delegates in Philadelphia and tens of millions of viewers at home.
The White House says Mr Obama has been working on the roughly 30-minute speech for weeks.
Yet this touchstone presidential moment has been a decade or more in the making.
The address will bookend Mr Obama's career-launching address to the Democratic convention in 2004, his contentious 2008 primary battle with Mrs Clinton and his eight years in office.
Aides said Mr Obama will make a familiar case for what has been achieved during his two terms, highlighting America's recovery from the Great Recession.
Mr Obama will also try to leverage his vast popularity among Democrats to unify a party scarred by the bruising primary campaign between Mrs Clinton and leftist Bernie Sanders.
The four-day confab in Philadelphia - the City of Brotherly Love - has so far been somewhat less than fraternal, with disappointed Sanders supporters periodically disrupting the proceedings with boos.