They entered the race late, but the two billionaires seeking the Democratic nomination are making up for lost time.

Together, Tom Steyer and Mike Bloomberg have poured nearly $200 million into television and digital advertising alone, with the former New York mayor spending an unprecedented $120 million in the roughly three weeks since he joined the presidential race. That's more than double the combined ad spending of every single nonbillionaire in the Democratic field this year.

"We've never seen spending like this in a presidential race," said Jim McLaughlin, a Republican political strategist who worked as a consultant for Bloomberg's mayoral bids in New York. "He has a limitless budget."

The question isn't whether anyone else will come close to matching Bloomberg's or Steyer's ad spending. Rather, it's whether all that spending is making any difference.