[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2008/images/08/25/art.billc.gi.jpg caption=" Bill Clinton would rather discuss economic issues than national security, sources say."]DENVER, Colorado (CNN) – Bill Clinton is perplexed and, frankly, not happy that he was asked to speak about national security Wednesday night at the Democratic National Convention and not about the economy, the issue that he rode to the White House at another time of economic peril, a source close to the former president said Monday.

Some close to Clinton are encouraging him not to stick with the night’s theme of national security and add language about the economy in his remarks, in a way that Sen. Barack Obama, the presumptive Democratic presidential nominee, would frame it, the source said. It’s no secret that Clinton considers himself a highly effective communicator on the politics of the economy.

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As word of his displeasure was reported Monday, aides tried to suggest it was being overblown. It’s a pattern strikingly similar to reports of Hillary Clinton’s unhappiness with the way she was treated by Obama during his running mate search, which has contributed to intense talk of tension between camps Clinton and Obama leading up to a convention that’s being billed as a chance at unity.

Another Bill Clinton associate contacted CNN to dispute one report that he is angry about his speaking assignment, but that source also said the former president “believes there would be a lot of power in a Clinton/Bush/McCain economic contrast and might mention that a bit anyway.”

If history is any guide, it’s unlikely the Obama staff will know exactly what Clinton will say before he says it.

Another Democratic source who is involved in reviewing the convention speeches this year, and has in years past, said that unlike most other speakers, Bill Clinton's speech generally “comes in when he does - on a detachable drive and into the prompter.”