* Biden is "last man in the room" with Obama
* Gaffes draw criticism, provide candor
* Friends say he has not ruled out a presidential run in 2016
By Jeff Mason
CHARLOTTE, N.C. Sept 6 (Reuters) - Joe Biden was a pragmatic choice for vice president: a U.S. Senate veteran with foreign policy expertise. Four years later, he is one of Barack Obama's most trusted advisers, helping the president on the world stage and with voters at home.
Biden, after three and a half years dotted with off-the-cuff remarks, will make the case for Obama's re-election at the Democratic National Convention on Thursday night in ways that few others can. And in doing so, he will put persistent rumors of his own departure to rest by accepting his party's nomination.
The former U.S. senator from Delaware has withstood frequent speculation - much of it from Republicans - that Obama would drop Biden in favor of his formal rival and popular secretary of state, Hillary Clinton.
White House and campaign advisers deny such rumors, and interviews with several of them before the party's convention this week revealed why: Biden is viewed as a true partner for Obama, helping him with key constituencies in government and on the campaign trail.
C oming on the heels of former President Bill Clinton's comprehensive pitch Wednesday n ight, sharing a behind-the-scenes account of his boss's presidency ma y be Biden's top task.
"With the possible exception of the first lady, there's no one who's been closer to the president who can tell firsthand the story of the first four years, and that's incredibly helpful to us," Obama's campaign manager Jim Messina said in an interview.
Aides say Obama and Biden are close, and the 69-year-old is firmly focused on getting his y ounger boss re-elected, traveling regularly to battleground states, shoring up support among the party's base, and raising millions of dollars for the campaign.
As a governing partner, the vice president oversaw implementation of Obama's 2009 stimulus package and steered White House policy on Iraq.
As a campaigning partner, Biden spearheaded a strategy to define Republican nominee Mitt Romney early in the election cycle. The vice president's five "framing" speeches in March and April on topics from tax policy to foreign affairs cri ticized the former Massachusetts governor long before the president started mentioning his opponent regularly by name.
Biden's trusted role and close relationship with his running mate evolved to its current state after the two men took office in January 2009.
"In many ways, when you think about it, they didn't know each other that well before all of this started," said one Biden adviser, noting that the two former senators had not served long in Congress together before the 2008 election cycle began.
"It really wasn't until they got to the White House and wound up in offices that are, you know, whatever it is - 30 feet or 60 feet apart - in meetings together multiple times a day that they really developed this relationship."
CLOSE RELATIONSHIP, GAFFE-PRONE
When Biden agreed to be Obama's running mate, the senator said he wanted to be the "last man in the room" with Obama as a governing partner, friends said. Biden would follow Obama's lead, even when they disagreed, as long as he had his say.
"I think one of the reasons they get along so well is the president stuck by his side of the deal," said Ted Kaufman, a friend and former chief of staff to Biden.
Tony Blinken, Biden's national security adviser, said the two men see each other several times a day, starting with an early national security briefing th at is the first of many mee tings throughout the day.
"Often, (Biden) will stay at the end of the meeting, and he and the president will have a couple of minutes to talk privately," Blinken said. "And those are very important, I think, moments where he is literally the last guy in the room."
That relationship has helped them navigate rough patches when the vice president's verbal gaffes have c reated u nwanted headlines.
Earlier this year, he disrupted a planned rollout of Obama's decision to support gay marriage by voicing his own support first in a television interview.
Last month at an event in Virginia with a partly African American audience, Biden declared that Romney wanted to put people back in "chains" - a metaphor he meant to use as a criticism of Romney's views on banking regulation.
The comment and its apparent reference to slavery drew pointed criticism from the Republican candidate and caused Obama's advisers to cringe.
"Joe Biden increasingly has been a liability for President Obama," said Brian Jones, a Romney adviser, who said Biden's missteps helped the Republican's campaign.
"Certainly when he has committed verbal gaffes in the past, it detracts from the president being able to deliver his message, so from that perspective, we welcome it," Jones said.
Obama campaign advisers do not welcome it, but they dismiss the effect of such gaffes, which they see as outweighed by his ability to connect with voters, especially working-class people in swing states such as Ohio and Pennsylvania.
"People trust him. They know he's going to say what's on his mind," Messina said. "We are better off with Joe Biden out there making the case, and we'll continue to put him out there as much as we can have him."
If the Democrats win the White House on Nov. 6, Biden's role and high profile will lead to questions about his own political future.
Friends and advisers said the lifelong politician had not ruled a 2016 run in or out.
"I think that he should sit down after the election and do what we always do and get the family and key friends together and look at 2016," said Kaufman, the former chief of staff.
"But there's nothing, absolutely zero to be done now."
Messina dismissed any suggestion that Biden was positioning himself now for a future run.
"If anyone in the world would see it ... it would be the president's campaign manager, and that has never once come up into my head," he said. "The vice president understands the most important thing for this country is to continue to move forward, and that means electing Barack Obama president."
Biden will work to advance that during his convention speech on Thursday evening. Meanwhile Clinton, the woman who was rumored to replace him on the ticket - and who could challenge Biden for the party's nomination in 2016 - will be on the other side of the world. The secretary of state is traveling in Asia.