On Capitol Hill, the Senate is expected to vote today to approve expanding embryonic stem cell research. But President Bush is threatening to issue the first veto of his presidency in order to block the legislation. A debate over stem cell research has split the Republican Party. Several prominent party members including former First Lady Nancy Reagan and Senate Majority Leader Doctor Bill Frist back the research. But many religious leaders who oppose abortion claim that conducting medical experiments on fertilized human eggs amounts to ending human lives.