Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE’s campaign and its allies are outspending their Republican counterparts by a factor of about five to one, according to a new analysis released Tuesday.

But the former secretary of State has failed to put away Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE, and many anxious Democrats are baffled as to why the race remains so close.

ADVERTISEMENT

Part of the reason may be that TV advertising — often the single biggest budget item within a campaign — is losing its effectiveness.

“It’s becoming more difficult to target voters,” said one Democratic strategist, who requested anonymity to speak candidly. “Voters are more cynical about ads because they have seen them for decades. Nothing is as effective as it used to be.”

The analysis published by NBC News on Tuesday, drawing on data from tracking firm Advertising Analytics, found that the Clinton campaign had spent $96.4 million on the airwaves against just $17.3 million from the Trump campaign.

When outside groups supporting Clinton’s candidacy were included, the total spend on her side reached $156.6 million. The comparable figure for all pro-Trump advertising was $33.6 million.

Clinton is a slight favorite in the race, but the huge disparity in spending has failed to break the contest open. Data website FiveThirtyEight gave Clinton a 56 percent chance of winning as of Tuesday afternoon, while the RealClearPolitics average of national polls showed her with an edge of about 1 percentage point.

Some Republicans argue that the closeness of the race — especially against a candidate with Trump’s vulnerabilities — is evidence of Clinton’s fundamental flaws as a candidate.

“She’s not up more because she’s disliked and distrusted,” said GOP consultant Rick Wilson, who is working with independent presidential candidate Evan McMullin. “With any other candidate than [Clinton], Trump would be down by 25 percent.”

Other experts highlight additional factors. One challenge for any candidate is the degree to which viewing habits have changed, with audiences fragmenting and many young voters, in particular, moving away from traditional TV viewing.

“There is no question that the return on investment for paid advertising continues to degrade from election to election, as it does for commercial TV advertising generally,” said Chris Lehane, a Democratic strategist who served in former President Bill Clinton William (Bill) Jefferson ClintonGOP brushes back charges of hypocrisy in Supreme Court fight Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE’s White House and on then-Vice President Al Gore Albert (Al) Arnold GoreCruz says Senate Republicans likely have votes to confirm Trump Supreme Court nominee 4 inconclusive Electoral College results that challenged our democracy Fox's Napolitano: 2000 election will look like 'child's play' compared to 2020 legal battles MORE’s 2000 campaign.

Even so, Lehane added, “for many, as inefficient as it is, there is still not a better option in terms of reaching voters, and so there is a default to paid TV advertising.”

This year, there is also the unique nature of Trump’s campaign to consider. The New York businessman has used skills honed over decades as a tabloid staple and a reality TV star to drive media coverage.

During the Republican primary, Trump and his allies were outspent by wide margins by three rivals: former Florida Gov. Jeb Bush, Florida Sen. Marco Rubio Marco Antonio RubioMurky TikTok deal raises questions about China's role Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Florida senators pushing to keep Daylight Savings Time during pandemic MORE and Texas Sen. Ted Cruz Rafael (Ted) Edward CruzThe Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy Murkowski: Supreme Court nominee should not be taken up before election Battle lines drawn on precedent in Supreme Court fight MORE.

An NBC News/SMG Delta analysis in early June found that Team Bush had spent approximately $82 million by that point, whereas Trump and his allies had spent less than $19 million.

“Earned media always trumps paid media,” said the Democratic strategist, “and Trump has mastered earned media in this election, for good and bad.”

A veteran Republican ad-maker, Fred Davis, agreed — and suggested this could be part of Clinton’s problem.

“He’s a walking attention magnet, and interesting,” Davis said via email. “She’s the past and relatively dull.”

Still, despite all the idiosyncrasies of this year’s race and the growing challenges of advertising effectively on television, few people argue that ads don’t matter at all.

Many of Clinton’s ads have been negative, including her most memorable spot, which shows children watching a TV screen of Trump making incendiary comments. While that ad has attracted praise, some Democratic strategists say Clinton needs to pivot and embrace a more positive message. These operatives point out that Trump’s disapproval ratings can’t go much higher and Clinton needs to work on her approval/disapproval numbers.

Yet Lehane argued that the ad campaign might have played a key part in keeping Trump’s approval ratings down. If things work according to plan, from a Democratic perspective, this could make victory all but impossible for the GOP nominee.

“Ads can have a compounding effect over time,” Lehane said. “Trump remains stagnant in the low 40s in part because his negatives limit growth with key voter cohorts.”

Clinton’s TV advertising appears, from anecdotal evidence at least, to have leaned heavily on a small number of ads. Independent experts say that finding the right balance between hammering a message home while not boring voters is a hard task.

“That is kind of an art,” said Travis Ridout, a Washington State University professor and the co-author of a book about campaign advertising.

“Repetition definitely is good, we know. But you do reach a point of diminishing returns. The difficulty is that political junkies might be seeing TV all day long and might be seeing tons of ads. And there may be another person only tuning in one hour a day. You shoot for the average voter.”

The belief that one can hit that target and transform the election may be overly optimistic, said the Democratic strategist who requested anonymity.

“It’s a mistake on the part of the campaigns to believe you can dig yourself out of a hole or bury your opponent simply be outspending them on air. It’s just not realistic anymore," the strategist added.