A majority of millionaire Republicans do not believe that Amazon has helped the U.S. Postal Service, according to the latest CNBC Millionaire Survey , while a vast majority of wealthy Democrats said the tech retailer has benefited the USPS.

President Donald Trump has made Amazon and its founder and CEO, Jeff Bezos, a repeated target of attacks. It seems to be working, and not just with his base of working-class voters.

The CNBC Millionaire Survey was conducted by the Spectrem Group in April to assess the investment attitudes and behaviors of U.S. millionaires. It studied 750 Americans nationwide with $1 million or more of investable assets. Respondents were both male and female with political affiliations to the Republican, Democratic and Independent parties.

Trump has lashed out at many companies, most recently Harley-Davidson on Tuesday, but Trump has been fixated on Amazon for far longer. In a series of tweets between late March and early April, he accused the company of paying “little or no taxes to state and local governments” and setting up The Washington Post, also owned by Bezos, as a de facto lobby for Amazon.

The president also blasted Amazon for profiting at the expense of the United States Postal Service, which briefly took a toll on Amazon shares. Trump said Amazon was using the USPS as its "delivery boy" and the practice was a "scam" that cost the Post Office "billions."

In one March tweet Trump remarked, "Only fools, or worse, are saying that our money losing Post Office makes money with Amazon. THEY LOSE A FORTUNE, and this will be changed."

The CNBC Millionaire Survey found that 72 percent of Democrats think Amazon has helped the U.S. Post Office versus only 48 percent of Republicans.

That wide gap between Democrats and Republicans on the issue was partially a function of wealthy Republicans not wanting to answer the question. Twenty-five percent of wealthy Republicans said Amazon has neither hurt nor helped the U.S. Post Office, while another 6 percent said they “don’t know.”

Joshua Tucker, a professor of politics at New York University, said "political cueing" can help explain the political divide on Amazon. “What you’re probably finding is when you have a complex question that people don’t have an opinion on, if they can cue on a political party, they will,” Tucker said.

Tucker said the media attention paid to the U.S. Post Office issue helps explain the wide political divide.

“I would go as far to say that if you had asked this question before any of this discussion of the tweets in the media, you probably wouldn’t have seen this difference,” Tucker said.

A Gallup poll released last weekend found 90 percent support among Republicans for Trump, with many GOP voters remarking that media coverage of Trump compelled them to support the president.