Consumer advocates have scored some surprising victories in the overhaul of financial regulations that’s gaining momentum in Congress, but amendments to be considered in the coming days will go a long way toward shaping the sweeping measure.

Some proposed amendments in the Senate could benefit financial firms, such as those that would limit states’ powers to oversee financial products and exempt car dealers from the authority of a new financial watchdog agency. Others would crack down even harder on Wall Street practices.

So far, Wall Street’s formidable lobbying power has not weakened the bill, as some observers expected. The Senate, for instance, soundly defeated a move by Republicans to…