Kiss Britney. Check. Write children’s books. Done. Endorse General Wesley Clark for President. Yup, did that too. In a strangely — or not so strangely — self-important letter made public Jan. 7, Madonna threw her weight behind Clark. If the pop star’s preachy move is any sign, this campaign season will see countless celebs join the outspoken ranks of Barbra Streisand. Not to be outdone, Republicans like Bruce Willis will likely stump for President Bush. But the real question remains: Can anyone top Madge’s eloquent gift of self-expression?