Jeb Bush takes part in ceremonies in Londonderry, New Hampshire, to remember the victims of the Sept. 11, 2001, attacks, on Sept. 11, 2015. Reuters

Jeb Bush is struggling in Iowa, but his campaign isn't giving up. Tapping the massive fundraising earlier this year that reaped more than $100 million, the former Florida governor's presidential campaign spent $5.89 million on Iowa advertising this week, with more ad buys expected to come.

"It's a muscular buy for a muscular story," Mike Murphy, chief strategist for Right to Rise USA, the super PAC supporting Bush that bought the ads, told the Des Moines Register. Bush has dropped in the polls from a high perch as the presumptive Republican front-runner in recent months, and the campaign is feeling the heat. His perceived front-runner status, even before he announced his candidacy, was partly fueled by the sheer amount of money he was going to raise for a presidential bid through his affiliated super PAC.

The first advertisement released teases the viewer with a silhouette of the candidate before ultimately showing Bush walking with hard hat-wearing workers and supporters. It touts his conservative record as governor of Florida: creating jobs, taking on unions, changing the education system and cutting government spending.

Bush has never been the front-runner in Iowa caucus polls, but he's certainly fallen far since April. In an average of polls, Bush was once second behind Wisconsin Gov. Scott Walker, but has dropped to seventh, according to poll averages in the state. That puts him behind not only Walker -- who himself has dropped to fourth in the state -- but also three nonpoliticians and a tea party favorite. Businessman Donald Trump polls first with 27.2 percent of the Iowa vote and former neurosurgeon Dr. Ben Carson is in second with 20.8 percent. They are followed by Texas Sen. Ted Cruz (7.8 percent), Walker (5.7 percent), former Hewlett Packard CEO Carly Fiorina (5.7 percent) and Bush's former protege, Florida Sen. Marco Rubio (5.2 percent).