WASHINGTON — Facing bankruptcy, the U.S. Postal Service is pushing ahead with unprecedented cuts to first-class mail next spring that will slow delivery and, for the first time in 40 years, eliminate the chance for stamped letters to arrive the next day. The estimated $3 billion in reductions, to be announced in broader detail on Monday, are part of a wide-ranging effort by the cash-strapped Postal Service to quickly trim costs, seeing no immediate help from Congress. The changes would provide short-term relief, but ultimately could prove counterproductive, pushing more of America's business onto the Internet. They could slow everything...