Possible Clues:

• Isaac's father, in the Bible
• A heartless old F1 driver, father of many
• He's tested in Genesis 22
• First name on Mount Rushmore
• He had a Lot to contend with
• Solver's Last Hurrah rating: Mark's bound to be first in race
• Plains of --, plateau near Quebec, scene of a battle in 1759
• With 39-Across, signer of the 23-/51-Across
• Jewish father puts fresh bar on some pork
• A support actor portraying Lincoln?