Minnesota Senator Paul Wellstone has pushed through an amendment that could prove critical to the prospects for the McCain-Feingold campaign finance reform package. Wellstone's provision would ban ads by special interest groups in the weeks leading up to an election. Critics on both sides of the aisle say the amendment may violate the right to free speech. And some of campaign finance reform's biggest foes voted for the amendment- hoping the constitutional questions it raises will weaken the final bill. Wellstone says his amendment is an important piece of campaign finance reform.