WASHINGTON - After months of partisan maneuvering, Senate passage of sweeping immigration legislation is virtually assured by Memorial Day. But that scarcely ends the struggle in Congress, given the vast differences between President Bush and House Republicans over the fate of millions of illegal immigrants. The substance of the Senate bill is unlikely to change significantly from the measure that was stuck in gridlock more than a month ago. It includes additional border security, a new guest worker program and provisions opening the way to eventual citizenship for many of the estimated 11 million illegal immigrants in the country. What...