> When did conservatives abandon the free market?

You're using terms incorrectly. Conservatism has nothing to do with free market.

The people who care most about free markets are liberals (called libertarians in the US).

Presumably you mean to say "Republicans". And your answer is "under Trump". But it's important to note that Trump merely took the Republican party back to its roots. Traditionally, Republicans were more protectionists than the Democrats. Regan changed that, and Trump reverted.

But what annoys me about people who criticize this change, is that it often comes from people who don't believe in free markets.

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As a side note, I think the reason Americans use these terms so wrongly is because of the 2 party system. It forces all ideologies into two camps and for Americans "conservatism", "libertarianism", "nationalism", "fascism" are all the same.