Many Republicans and conservatives have criticized Donald Trump since he rose to first place in the polls — but for two months, none of them put up serious cash to try to stop him.

On Tuesday, that changed. The Club for Growth — an anti-tax, anti-spending conservative pressure group — announced it would spend $1 million on anti-Trump ads in Iowa. Here's a look at one, which says Trump has a "very liberal" record and is "playing us for chumps," and calls him "just another politician."

This is the first significant anti-Trump ad buy, and the political world will watch with bated breath to see if it helps knock Trump out of the lead in Iowa — and also to see how Trump, who hasn't run paid TV ads yet, will respond to a challenge on the airwaves.

But it's no surprise that the Club for Growth is taking the lead. For months now, Trump and the club — which is mainly funded by wealthy investors and financiers — have been at each other's throats, publicly feuding on Twitter. On the surface, the dispute is about what happened around a meeting months ago, after which the club's president asked Trump for a $1 million donation.

In reality, though, the feud gets to the heart of why the billionaire's candidacy is so dangerous to the conservative electoral coalition. The club's mission has long been to push the GOP far to the right on economic issues — slashing taxes and spending as much as possible. But Trump has pledged to protect Social Security and Medicare spending, and says the wealthy should be taxed more.

That makes his candidacy incredibly dangerous to both the club and the current orthodoxy on tax and spending issues that exists across the GOP — an orthodoxy that the club helped bring about, and tries to enforce.

The Club for Growth has tried to push the GOP far to the right on economic policy

Despite keeping a low profile with the general public, the Club for Growth has gradually become an important player in GOP politics by funding primary challenges against politicians the group deems as tax-hiking, big-spending RINOs (Republicans in name only).

The group's origins date back to the early 1980s, when wealthy investor Richard Gilder and several of his friends on Wall Street joined up to interview political office seekers about their views on economic policy. If Gilder and his friends liked what they heard — the bigger the tax and spending cuts, the better — they'd hand over campaign donations.

"If you want to run as a Republican, you are going to have to be for smaller government, lower taxes, free trade"

Eventually, however, the group's members became convinced that the Republicans they were helping elect to Congress were becoming too comfortable with the status quo. To prevent this, the group would target moderates in primaries, spending big to support conservative challengers. "We are saying that if you want to run as a Republican, you are going to have to be for smaller government, lower taxes, free trade," the club's then-president, Steve Moore, told the Washington Post in 2000.

Eventually, some of the club's challengers, like now-Sens. Mike Lee in Utah and Marco Rubio in Florida, started to defeat their moderate, establishment-supported rivals. And the mere threat of an expensive, well-funded primary challenge caused many Republicans to move to the right on fiscal issues. "I always say politicians are cowards, and they really are. We say we're going to run someone against them, and they start wetting their pants," Moore bragged to the New York Times Magazine in 2003.

Sometimes this strategy seemed to backfire. In 2009, Sen. Arlen Specter of Pennsylvania avoided a repeat GOP primary challenge by the club's then-president, Pat Toomey, by switching parties and becoming a Democrat — and then provided one of the crucial 60 votes to pass Obamacare months later. And far-right club-backed challengers like Sharron Angle in Nevada and Richard Mourdock in Indiana have won their primaries, and lost badly to Democrats in general elections that were supposed to be competitive.

But overall, the party has moved in the direction the club wants. Republican politicians have become more united in opposition to tax hikes, and in support of entitlement-cutting budgets like Paul Ryan's (which despite trillions in cuts is still too moderate for the club). Specter may have voted for Obamacare, but Toomey now holds his seat. This change in the GOP isn't entirely due to the club, but the group is perhaps the most prominent and best-funded player that's trying to scare congressional Republicans away from moderating via primary challenges.

Donald Trump's economic policies are the exact opposite of what the club wants

During Trump's presidential campaign, the mogul has gained notoriety for his pledge to deport 11 million unauthorized immigrants, and for his claims that the Mexican government is sending criminals and rapists across the border. This has led many to view him as a far-right fringe candidate.

But it's not so simple. Indeed, on the tax and spending issues that the club has always cared about most, Trump is a downright heretic in the modern GOP. He's pledged he'll make "no cuts to Social Security, Medicare and Medicaid." He's said he'll hike taxes on the wealthy, especially hedge fund managers, whom he refers to as just "guys that shift paper around" and "get lucky."

Trump has called the club "pathetic" and "phony," and suggested it's a "scam operation"

And — worse yet for the club — there's some evidence that his views are quite popular among Republican voters. A 2014 Gallup poll found that 45 percent of Republicans thought the wealthy pay too little in taxes, compared with just 21 percent who thought they pay too much. Similarly, more Republicans want to raise spending on Social Security and Medicare than cut it. And when Theda Skocpol and Vanessa Williamson interviewed Tea Party supporters for a political science study, the people they talked to "were very anxious that Social Security and Medicare be maintained."

The wealthy elite GOP donor class that funds campaigns — and the think tanks that help mold conservative ideology, and the advocacy groups that enforce ideological discipline — have, so far, succeeded in preventing Republican politicians from adopting these views, even though they seem rather popular.

But Trump, who's self-funding his campaign, doesn't need to raise money from these sources. He's free to take whichever positions he thinks will win him the most votes.

Donald Trump has been fighting with the club for months

So when Trump announced his presidential candidacy on June 16, the Club for Growth immediately released a statement trashing him. Citing the mogul's past support for single-payer health care and a huge tax on wealth, club president David McIntosh said Trump was "not a serious candidate for president."

But Trump soon revealed that just weeks earlier, McIntosh had come to meet him in New York — and, in a letter soon afterward, had asked him for a $1 million contribution to the club. Trump, who didn't pay up, tried to argue that the club was opposing his candidacy in revenge. In a barrage of tweets, he called the club "pathetic" and "phony," and suggested it's "a scam operation." He even tweeted out the letter from McIntosh asking for the money.

.@club4growth should release the letter they sent me asking for $1,000,000. When I said no, they came out against me. A scam operation? — Donald J. Trump (@realDonaldTrump) September 7, 2015

This is mainly a red herring — an attempt at spin by Trump. The club's views on economic policy are well-established, and have been for decades. When Republicans run in primaries with a platform like Trump's, the club tries to take them down. That's its whole reason for being.

The true conflict here is a struggle for control of GOP orthodoxy. Conservatives have had a stranglehold on Republican economic policy ideas for years now. Tax cuts for the rich and entitlement cuts for average Americans have become the party's platform, despite the dubious electoral benefits of such an approach. This has been great for the Club for Growth and its wealthy backers — though they of course still see the establishment as full of RINOs, and want the party to do much more. The rise of Trump puts this triumph at risk — so he must be stopped.