Can someone TLDR me on why Trump is so fond of protectionism and tariffs?

do you guys honestly not remember 2016 lol?

Bernie and the Trumptards came after Hillary on the TPP, at some point she did declare she was against it, but only because Bernie and Trump went after her over it repeatedly and there's some weird anti-trade worldview growing in America now.

Trump 100% ended the tpp:

Twelve countries participated in negotiations for the TPP: the four parties to the 2005 Trans-Pacific Strategic Economic Partnership Agreement and eight additional countries. All twelve signed the TPP on 4 February 2016.[25] The agreement would have entered into force after ratification by all signatories, if this had occurred within two years. If the agreement had not been ratified by all before 4 February 2018, it would have entered into force after ratification by at least 6 states which together have a GDP of more than 85% of the GDP of all signatories. The withdrawal of the United States from the agreement in January 2017 effectively ended any prospect of the agreement entering into force. In response the remaining parties successfully negotiated a new version of the agreement that lacked the 85% GDP threshold, the CPTPP, which entered into force in December 2018.

On 23 January 2017, US President Donald Trump signed a presidential memorandum to withdraw the United States' signature from the agreement, making its ratification as it was in February 2016 virtually impossible.[27]

Here's Trump going after her over it:

https://www.politifact.com/factchecks/2016/sep/27/donald-trump/donald-trump-says-hillary-clinton-lauded-controver/

The GOP themselves ran ads on it:

https://www.cnn.com/2016/06/28/politics/donald-trump-hillary-clinton-tpp/index.html