TUCSON, Ariz. - Rick Santorum took a pre-debate dig at his GOP rival, claiming Mitt Romney's new tax plan looks an awful lot like the one Santorum has already rolled out.

"I just saw today that Governor Romney announced that he was going to be lowering the tax rates to, well, the tax rate I proposed," Santorum quipped during a Tea Party rally in Tucson.

"Welcome to the party, Governor. Great to have you along."

Romney pledged Wednesday to slash tax rates for all Americans by 20% just hours earlier, saying it would not add more debt since he would cap deductions and exemptions for the wealthy.

The proposal could be an attempt to bring renewed focus on the economy, as opposed to the social issues Santorum is connecting with conservatives on.

But the former senator also struck a chord here on illegal immigration. The crowd rose to their feet and erupted with applause after Santorum tied the issue to his own family's history.

"My grandfather came to this country in 1925. He came by himself. He left his family behind, his young children, his wife, he left them after having served in WWI," Santorum explained.

"But he came to America, sacrificed 5 years of his life. Worked in the auto factories a couple of years, and then in the coal mines, in a company town for 3 more years, until he was able to refill the requirements and bring the rest of the family over," he added.

"So I understand the heartache of well, what happens if you send people back? They're going to be separated from their family. That's right. America is worth it, to do it the right way."