Washington CNN  — 

The barrage begins now.

Less than two months before the Iowa caucuses, the Democratic presidential contenders are ramping up their spending with television ads that sell themselves and take aim at President Donald Trump.

Massachusetts Sen. Elizabeth Warren, who has slipped in some recent polls, has reserved $7.4 million in television advertising in the four early nominating states of Iowa, New Hampshire, Nevada and South Carolina as of Tuesday, according to a CNN tally of advertising from Kantar Media’s Campaign Media Analysis Group, or CMAG.

Most of the new spending – $3.1 million – will hit the airwaves in Iowa, a state key to Warren’s presidential ambitions and where she has recently lost ground to South Bend, Indiana, Mayor Pete Buttigieg. Former Vice President Joe Biden, meanwhile, also has dramatically upped his advertising, plowing nearly $2.4 million into Iowa, where he has just wrapped up an eight-day bus tour.

CMAG’s tally shows Biden also plans to spend $1.8 million in South Carolina, a place crucial to his presidential campaign. Biden’s strong support among African Americans who make up 60% of the state’s Democratic electorate could provide a firewall should he falter in Iowa and New Hampshire.

And Vermont Sen. Bernie Sanders, who had already spent more than $4.6 million in Iowa headed into this week, just put his sixth ad into rotation in the Hawkeye State.

Candidates hope the advertising will help them break through the noise of a presidential impeachment and make their pitches to the voters who kick off the 2020 nomination battle. But the commercials also provide the name recognition that helps candidates meet the Democratic National Committee’s polling and fundraising thresholds to participate in nationally televised debates. This week, businessman Andrew Yang notched his fourth qualifying poll for next week’s debate in California. He’s also spent about $3 million in advertising in Iowa through early this week.

New Jersey Sen. Cory Booker, who has spent no money on TV advertising, still hasn’t made the debate cut.

On the air

Warren’s planned $7 million advertising blitz through the fourth week of February is more than five times the amount she spent during the first 11 months of this year. Her latest ads tout her work to create the Consumer Protection Financial Bureau and the anti-corruption message that is central to her presidential campaign. In one ad, she charges, corruption is “breaking our democracy” as an image of Trump flashes on the screen.

Her advertising comes as Warren has seen her support drop in recent national polls. A Monmouth University poll released this week put her at 18%, down from 23% in September. She also slipped in CNN’s poll with SSRS released in late November, from 19% in October to 14%.

Dave Peterson, a political scientist and pollster at Iowa State University in Ames, said his polling – which includes surveying the same likely caucus-goers repeatedly over several months – shows an unsettled race with a “chunk of Iowans drifting between candidates” and Warren losing ground to Buttigieg.

He said the new crop of ads may help “remind people what they like about her.”

“But my concern for Warren is: Are they too little too late?” Peterson said. “The time to stop the drift was about a month ago. Once people have moved on from a candidate, do they go back?”

A Warren campaign spokesman this week declined to discuss advertising strategy.

Biden, for his part, began airing a 30-second ad in Iowa on Tuesday that assails Trump as a “president the world is laughing at.” The ad, which the Biden camp first released as an online video last week, uses a clip of world leaders caught on a hot mic appearing to joke about Trump’s behavior at a NATO gathering. The video quickly racked up millions of views.

Super PAC help

As Biden’s campaign targeted Trump, a super PAC supporting his candidacy, Unite the Country, took to the air in Iowa this week with a biographical commercial. Entitled “Courage, it uses audio from Biden speeches to highlight his support of same-sex marriage and his work to pass an assault weapons ban.

A super PAC also is attempting to boost Booker’s standing in Iowa.

An ad by the pro-Booker United We Win touts his credentials as a senator and former Newark, New Jersey, mayor and takes a not-too-subtle dig at Buttigieg, often mentioned as having received a prestigious Rhodes scholarship. The United We Win spot reminds viewers that Booker enjoys the same distinction. Booker, the ad’s narrator says, is the “Rhodes Scholar mayor” equipped “to beat Donald Trump.”

Booker has made repeated dire appeals to supporters for the money to air commercials to help him qualify for the Democratic National Committee’s next debate December 19 in Los Angeles. The cutoff deadline is Thursday.

“We have to run ads,” Booker said to CNN’s Don Lemon this week. “We have seen everybody running ads gin up their polling numbers and get on the stage.”

So far, Biden, Sanders, Warren, Buttigieg, Yang, Minnesota Sen. Amy Klobuchar, and billionaire Tom Steyer have qualified for next week’s debate.

Billionaire big spenders

For Steyer, a former hedge fund manager from California, his participation in the debate has come at a high price: He has spent more than $81 million on TV ad bookings, CMAG’s data show.

But former New York City Mayor Michael Bloomberg, who entered the Democratic presidential race on Nov. 24, has eclipsed even Steyer’s investment in the Democratic nomination battle. This week, Bloomberg topped the $100 million mark in television buys. That’s more than three times the television ad spending by the four top-polling Democratic candidates combined.

While his rivals fight for primacy in Iowa, Bloomberg has bypassed the early states and instead is staking his candidacy on Super Tuesday in early March, when more than a dozen states are up for grabs.

CNN’s Grace Sparks and Rebecca Buck contributed to this report.