Only billionaire Tom Steyer, at $7.1m, has spent more on TV ads in Iowa, according to Kantar/Campaign Media Analysis on FiveThirtyEight.
Sanders, who has raised $10m more than Buttigieg this cycle, is just slightly behind him in the state, spending $2.0m on Iowa TV ads.
Biden has spent $820k and Warren just $200k on Iowa TV so far.
Buttigieg’s campaign credits a strong October debate performance and subsequent post-debate outreach as a key factor for the rise in the polls.
“A lot of people don’t know who Pete is, at all,” a campaign spokesman tells Axios. “So we are going to continue to find ways to introduce him to new audiences.”