If you want to win the MidWest you have to oppose FTA's, but every single large corporation and wealthy donor supports FTA's. So ever since Bill Clinton, both parties have tried to obfuscate their position on the issue.

President Trump's position on FTA's is complicated.
He did tank TPP, but he's soft on TTIP.

President Donald Trump is willing to reopen negotiations with the European Union over the stalled Trans-Atlantic Trade and Investment Partnership agreement, which stalled following his election, according to U.S. Commerce Secretary Wilbur Ross.

“He terminated the trans-Pacific deal; he didn’t terminate TTIP,” Ross said in an interview with Bloomberg Television on Thursday. “That was meant quite deliberately and quite overtly as a message that we’re open to discussions with the European Commission.”

But he renegotiated NAFTA, right? Well, maybe not.

A while back I noted that the new USMCA treaty (i.e., NAFTA 2.0) would not increase American GDP. The government’s own analysis projects a GDP decrease of 0.12 percent, but then adds back 0.47 percentage points because they figure that newfound certainty in things like intellectual property rules will increase investment. This suggests that we might be better off just adopting the IP rules and skipping the rest.

But wait! Jeffrey Schott of the Peterson Institute for International Economics—normally the kind of place that loves trade treaties—says that even this is bogus:

Some supporters of the deal say it provides new rules that will benefit the U.S. But those “new” rules aren’t new. Rather they mirror provisions affecting labor, the environment and e-commerce from the revised Trans-Pacific Partnership that have been carried out by Mexico and Canada since that accord went into effect on Dec. 30, 2018. Trump withdrew from the TPP, but Canada and Mexico remained in it, and already apply these provisions in trade relations with the U.S.

So essentially Trump made a big deal about a small thing, and hopes that no one notices.

As for the Democratic candidates, with two notable exceptions, their positions on FTA's is equally hidden.

Toward the end of his vice presidency, Joe Biden was a prime player in the administration’s bid to win support for the Trans-Pacific Partnership, the failed trade deal that was supposed to be the crowning achievement of Barack Obama’s presidency-long “pivot to Asia.”
...On the eve of the first presidential-primary debates, however, Biden’s 2020 campaign wouldn’t say whether he still supported the deal.

Biden is far less than surprising. However, there are surprises with the other candidates.

Of the people who were firm in their answers, former Representative John Delaney of Maryland is the only one who said yes.

Several candidates’ campaigns didn’t provide answers on their current position on TPP despite repeated requests: South Bend, Indiana, Mayor Pete Buttigieg; Senator Amy Klobuchar of Minnesota; and Representative Tulsi Gabbard of Hawaii.

Gabbard's non-answer is both surprising and disappointing.

Though TPP itself never came up for a vote on Capitol Hill, in 2015 a related bill called Trade Promotion Authority did. It allowed Congress to take a simple initial yes/no vote on approving trade deals, rather than having each section of an agreement subject to debate. In practice, voting for TPA was largely seen as a vote for TPP, because it was passed with the understanding that Obama would immediately use it to send his trade deal up for a final vote.

Neither Warren nor Sanders voted for TPA.

Sanders we knew about, but Warren is a pleasant surprise.

Warren and Sanders aren’t the only senators opposed to TPP. Senator Cory Booker of New Jersey stands by his opposition to TPA and TPP, said his press secretary, Sabrina Singh. TPP “put large corporations before workers and would have led to the decline of U.S. manufacturing,” Singh said. According to a spokesperson, Senator Kirsten Gillibrand of New York, who also voted against TPA and opposed TPP, “believes U.S. participation in any trade agreement needs to have a real strategy behind it.” It “must hold bad actors accountable, promote fair trade, protect American workers and the environment, and deliver real economic growth to middle-class families,” the spokesperson explained.

Other candidates weren’t in Congress for the TPA vote, and some may not have taken a position on TPP until now. Senator Kamala Harris of California opposed TPP when she campaigned for the Senate in 2016, “pointing to its lack of worker protections,” said her press secretary, Ian Sams, adding that she wouldn’t join the agreement as president.

None of these three I believe, but it is nice to see them oppose these FTA's in public.