WASHINGTON (CNN) - Billionaire businessman Bob Johnson, a close adviser and friend to Sen. Hillary Clinton , launched a campaign Wednesday to persuade Sen. Barack Obama to offer the vice presidential slot on the Democratic ticket to Clinton.
Johnson told CNN's "American Morning" that Clinton knows about his push but "she didn't direct me to do it."
A day after the final two primaries, Johnson sent a letter to House Majority Whip Jim Clyburn on Wednesday to lobby the Congressional Black Caucus to endorse Clinton as Obama's running mate. He said it needs to be done for the sake of party unity.
"There's no question that Sen. Clinton will do whatever she's asked to do for the party and she will certainly ... entertain the idea if it's offered," Johnson said.
In his letter directed at the Congressional Black Caucus, Johnson wrote:
"As African Americans we agree that the stakes in this election are far too high to take any chances that this party will not be unified from the top to the bottom in our effort to gain control of The White House."
He further wrote:
"You know as well as I the deep affection that millions of African Americans hold for both Senator Clinton and President Clinton. ... But most important, we need to have the certainty of winning; and, I believe, without question, that Barack Obama as President and Hillary Clinton as Vice President bring that certainty to the ticket."
Johnson, who founded Black Entertainment Television, also owns the Charlotte Bobcats basketball team.
He told CNN he was not trying to limit Obama's options, or force him to pick Clinton.
"My letter was not a pressure letter," he said. "This is Sen. Obama's decision.
"If the Congress members can come together and agree as I do that it would be in the best interest of the party to have Sen. Clinton on the ticket, they carry that petition to Sen. Obama," he said.
"This is not a pressure. This is elected officials giving their best judgment."
Obama clinched the Democratic presidential nomination on Tuesday night, according to CNN estimates of the delegate count.
He praised Clinton in a speech on Tuesday evening and said she will be central in the battle for universal health care and efforts to transform energy policy and lift children from poverty.
But in her speech after winning the South Dakota primary, Clinton said Tuesday night she would make no immediate decision on her next steps.
Obama and Clinton spoke by phone for a few minutes early Wednesday. He told her he wants to "sit down when it makes sense for" her, said Robert Gibbs, an Obama spokesman. She indicated she believed that would happen soon, Gibbs said.
Johnson created a stir and drew wide criticism in January for comments he made at a Clinton campaign stop in Columbia, S.C., that some interpreted as a reference to Obama's acknowledged drug use as a teenager.
In defending the Clintons' record on civil rights, Johnson said, "To me, as an African-American, I am frankly insulted that the Obama campaign would imply that we are so stupid that we would think Hillary and Bill Clinton, who have been deeply and emotionally involved in black issues since Barack Obama was doing something in the neighborhood - and I won't say what he was doing,
but he said it in the book - when they have been involved."
Many people believe Johnson was referring to Obama's drug use, which the senator publicly wrote about in his memoirs, though Johnson later said he was not.