As one might guess from his name, Agnew was of Greek heritage. His father was Theodore Spiros Agnew (formerly Anagnostopoulos), who immigrated to the United States from Greece in 1897.
And like Barack Obama, Agnew's father was not a U.S. citizen when Agnew was born. To evidence this, I offer the Agnew family's entry in the 1920 U.S. Census (see lines 72-75), where just three lines above the entry for one-year-old Spiro Agnew, Theodore Agnew's citizenship is clearly listed as "Alien":
Under the Twelfth Amendment to the U.S. Constitution, "no person constitutionally ineligible to the office of President shall be eligible to that of Vice-President of the United States." Ergo, the Vice-President must be a natural born citizen, just like the President.
Agnew's Greek heritage was conspicuous (especially given the name "Spiro Agnew"). His father's status as an immigrant was hardly obscure; to the contrary, his immigrant background helped him in becoming Nixon's running-mate.
And yet, Agnew was never accused of not being a natural born citizen. Nor was his Constitutional eligibility ever challenged on the grounds of his father's citizenship. Nor was his eligibility ever doubted on the grounds that he may have possibly inherited Greek citizenship through his father.
Spiro Agnew had a non-citizen father, and yet he was a natural born citizen. That is historical fact. To apply a different and novel test to Barack Obama, when the only difference between the two is that Agnew's father was from Greece whereas Obama's father was from Kenya, is simply inconsistent and hypocritical, and reeks of being a double standard.