Newswise — Despite the growing barrage of attack ads against Republican frontrunner Donald Trump, most of which are being financed by GOP supporters, Trump’s lead in the national polls continues to rise. Texas A&M University Professor of Communication Kirby Goidel says the ads may have come too late to hurt Trump’s chance to win the nomination—though the race could end in a contested convention—but they may affect his chance of winning in November.

Trump’s loss Tuesday night to Ted Cruz in the Wisconsin primaries could be an indication that negative ads are impacting his campaign, Goidel says. “It suggests negative ads are having some effect, however it was the ads plus media – conservative talk radio in Wisconsin has been decidedly anti-Trump.”

He adds the loss can also be partially attributed to demographics. “Fewer less-educated white voters and, perhaps surprisingly more religious voters, may have worked against him as well. Wisconsin never looked very promising for Trump and, in the end, it wasn’t.”

Regardless of last night’s loss, though, Trump is still hanging onto his lead in national polls.

“Recent estimates say that anti-Trump ads have aired in over 53,000 spots at a cost of nearly $67 million,” says Goidel, a Fellow at Texas A&M’s Public Policy Research Institute, whose comments on Trump represent his scholarly interest in the unprecedented campaign. “And yet, Trump’s support appears to be growing, even when the negative ads are increasing.”

Negative Trump ads have run the gamut including attacks on his failed business ventures, accusations that he’s not a true conservative, even a hit on his wife Melania. Social media is crawling with anti-Trump propaganda, including use of the popular Twitter hashtag #NeverTrump.

So how is Trump growing or maintaining his lead in the face of such widespread attacks?Goidel, says there are several possible reasons: first is that Trump is getting more free airtime than any other candidate, by a mile. “Trump has spent far less on advertising than his opponents, but he’s received $1.8 billion in free media airtime, more than all the other Republican candidates combined,” he notes, citing a New York Times blog. Hillary Clinton shows at a distant second with $746 million in free media time.

“Trump attracts eyeballs and because of that, media has him on as much as possible,” Goidel explains. “Often he’s calling in, which is a good thing for him; with phone interviews, it’s more difficult for the host to interrupt, so he just goes on and on saying whatever he wants. Not only can he respond to attacks, he can do it for free -- the media is giving him a free pass.”

Second, negative ads are hit-or-miss, Goidel asserts, adding it’s wise to run ads in test markets before they are used. “More often these days, online research is used to see if ads are effective.”

He says ads impact different target groups in different ways. “Independents will react to the same ad in a different way than Republicans. This is why targeting ads to different groups of voters is so important.”

Goidel points to several Trump attack ads which have tested well, according to Ace Metrix. Scoring high points with Independents are the ads “Talk Talk Talk,” “Bob” and “Big Money.” “Talk Talk Talk” also scores high with Republicans, along with “For Our Jobs,” “Plain Wrong” and “Nothing Conservative.”

Ads that score low for Independents include “Secret,” “New York Values” and “Playing Trump,” which also scores low with Republicans, along with “The Best Words,” “Democrat” and “System.”

Goidel says another reason Trump seems unfazed by negative ads is because he has excelled at defining his brand. “Once a brand identity is established, it's hard to take apart. There’s no doubt Trump has connected to his supporters, they are incredibly loyal now. His opponents’ best scenario is to keep him from gaining new supporters.”

Where the negative ads may end up hurting Trump is if he makes it to the general election, Goidel asserts.

“Trump’s unfavorable numbers seem to be increasing,” he says pointing to a poll showing 63.3 percent of those surveyed rated him “unfavorable.” If he were to face off with Hillary Clinton in the general election, this poll shows Clinton has a marginal lead. And Trump has a “problem with women,” Goidel notes, pointing out an NBC/WSJ national poll from March in which 47 percent of females surveyed they say cannot see supporting Trump.

The attack campaign against Trump goes to show there is no “magic bullet” when it comes to political advertising, Goidel says. “You can’t just run negative ads and win.” And, he notes, the notion that the more money candidates spend, the better their chances at winning is not always true – “Jeb Bush spent more on advertising than anyone.”