They are tired of the corruption seeping from every part of his administration. But of greater significance is that Democrats themselves have Clinton fatigue. They are tired of having to reveal their hypocrisy as they support him. Liberal women, for example, have been remarkably silent about Clinton's abuse and harassment of women. Because having power, not upholding principle, is their true goal.
Democrats are tired of the influence peddling and financial shenanigans.
And some Democrats are even tired of the lies. This Clinton fatigue puts Al Gore in an extremely awkward position. His loyalty to Clinton, from which he cannot gracefully disengage himself, leaves him suspect in the minds of many. And his own violations of campaign contribution laws suggest that the acorn has not fallen far from the tree. And if Gore is unable to escape the Clinton taint, even the standard Democrat issues like Social Security will not help.