Good supply-side cred for the senator. From the press release:

“I am proud to support John McCain for president,” said Jack Kemp. “John McCain is the only candidate who can be trusted to cut taxes, eliminate wasteful spending and enact conservative pro-growth policies to expand the economy. John McCain is the best choice to lead America to a more prosperous and secure future.”

Nothing about immigration here, but I suspect it played a role in Kemp’s endorsement.