The first thing to remember is that the New Deal was not one law or even one program. It was so broadly encompassing that it’s more comparable to a party platform.

FDR’s running mate, John Nance Garner, opposed it because of how much deficit spending it would require. The most consistent message from conservatives was: “The nation just a ton of money and you want to spend money we don’t have to benefit the people who create the least wealth?”

Ironically, there was also a great deal of opposition from the people who were supposed to benefit from the New Deal. The agricultural center of America had been hit by the consequences of several bad decisions right as the stock market crashed. The Midwest had been over-farmed for a couple decades, destroying the ecosystem and bringing on the Dust Bowl. This over-farming also had a detrimental effect on grain and livestock prices.

Even if the stock market hadn’t crashed, a depression would have happened in the Midwest because farming practices, which had been highly profitable during WW1, were untenable in the long run.

Part of the New Deal created public works projects (highways, bridges, etc.) that would allow some of these ruined farmers to shift careers. That was unpopular enough, partly because they were transitioning from business owners to government employees and partly because many saw it as charity. However, another program bought thousands and thousands of heads of cattle with government money and then just slaughtered the cows and dumped them in mass graves. This was done to get livestock prices back up. Many farmers saw it as a waste of good cows (“If we can’t sell them, can we eat them?”) and many politicians thought it was burning money.

On the other side, there was Huey Long. Long wanted the New Deal to be an even bigger program of wealth redistribution. His public opposition to Roosevelt was a shade off of hardline Marxism. He wanted more assistance to the poor and guarantees that black Americans would get the same payments as whites.

Roosevelt famously said that Douglas MacArthur and Huey Long were the two most dangerous men in America. So, Long was by no means fringe.

There was more, because the New Deal was sweeping, but those were the three biggest objections: it’s too expensive, it makes people dependent on the government, it doesn’t help the poor enough.