The impeachment hunt produced more casualties among the pursuers than among the prey, returning many unwillingly to private life. In the House that impeached him, Republicans lost two seats. In the Senate they went from five up to deuce. Clinton's wife won a seat there. Bush must know there's no hook big enough to yank Bubba entirely off the stage, but continuing to prosecute him would only give him a brighter spotlight.
TV loves nothing more than someone famous in the docket.
During a Clinton State of the Union speech, the networks kept a crawl on the bottom of the screen with updates on the O.J. jury deliberations. Clinton's trial would be a crawl on the bottom of the screen of the Bush presidency. Bush needn't worry that a pardon would move impeachment to the second paragraph of Clinton's bio. On the contrary, it would seal the Nixon comparison with Clinton the only other President to be pardoned. And it would make Bush seem more statesmanlike.