Shares of General Motors Corp and Ford Motor Co tumbled on Wednesday as mounting political opposition cast doubt over a proposed $25 billion government bailout for the U.S. automakers, Reuters reported. Shares of GM dropped more than 15 percent to a 66-year low, while Ford shares tumbled 23 percent to their lowest level in 26 years. The stocks extended declines after the chairman of the U.S. Senate Banking Committee said it looks unlikely Congress will come to agreement this week on an assistance package for the struggling U.S. auto industry. "I'm anxious to see something happen," Connecticut Democrat Christopher Dodd told reporters. "But frankly, the idea that there's going to be a bill, I think, is remote." U.S. auto executives headed to Capitol Hill for a second day to argue their case for the aid package which they say is imperative for the industry to survive. Barclays Capital analyst Brian Johnson said the prospect of a compromise between lawmakers remains "elusive" before a potential Senate vote this week. "Assuming defeat, GM would have to 'run on fumes' until the next Congress and administration, unless Congress were to reconvene in December to address emergency compromise legislation," Johnson said in a research note.