This post has been updated with even more recent polling showing Republicans have turned against the notion of free trade .

Here's the latest example of how 2016 is re-scrambling the Republican Party: Vulnerable Senate Republicans are starting to side with Donald Trump (and Democrats) by opposing President Obama's signature trade deal.

Yes, that's weird. Here's why:

1) As a general rule, Republicans like free trade. They say opening up our borders boosts grows the economy and boosts America's standing in the world. Republicans in Congress were the ones who carried the votes last summer to give Obama the authority to negotiate trade deals, including the 12-nation Pacific Rim deal he wants Congress to pass this year. So you might not expect Sens. Patrick J. Toomey (R-Pa.) and Rob Portman (R-Ohio) to say they can't support the Trans-Pacific Partnership. But that's exactly what they're saying.

"We should dump the TPP and return to the negotiating table to get an agreement that would create jobs and economic growth here at home," Toomey wrote in an op-ed in the Pittsburgh Post-Gazette on Tuesday.

Like many mainstream Republicans, Toomey is on record praising past trade deals. He wrote a book saying as much. He even warns in this op-ed if international trade stops, it could be a "disaster" for low-and middle-income families.

Same with Portman. Before becoming a senator for Ohio, he was literally the nation's top trade representative. In February, he said he won't support the TPP because "it doesn’t provide that level playing field."

We should mention that both senators are in heated reelections in states that tend to lean Democratic in a presidential year. Traditionally, Democrats are wary of free trade, especially blue-collar Democrats who live in Ohio and Pennsylvania. So these senators' giant step away from the TPP may be out of electoral necessity.

But were Democrats really going to vote for Toomey and Portman in significant numbers anyway? If we assume they weren't, that brings us to the next weird bullet:

2) The GOP base is becoming openly wary of trade.

And you can probably (at least this year) thank Trump for that.

From almost the beginning of his campaign, Trump has sounded more like Sen. Bernie Sanders (Vt.) than House Speaker Paul D. Ryan (R-Wis.) when he talks about trade. He's even threatened to back out of the North American Free Trade Agreement signed by President Bill Clinton.

"It's almost as though they want to protect the world and they don't care about our workers," Trump said of free trade supporters while speaking at a closed manufacturing plant in New Hampshire recently.

Republican presidential candidate Donald Trump brought his anti free trade message to supporters at a closed manufacturing plant in Manchester, N.H., June 30. (Reuters)

As my colleague Philip Bump has pointed out, Trump's opposition to free trade is savvy. He appears to have tapped into an anti-populist sentiment on the right that's manifesting itself on trade. And now he's helping to grow that.

A survey out Thursday by Pew Research Center shows 68 percent of Trump supporters think trade free trade agreements have been a bad thing, while just 26 percent say the deals have been a good thing.

And things are moving quickly. In May 2015, a month before Trump announced his candidacy, 51 percent of Republicans said free trade agreements have been a good thing for the U.S., while 39 percent said they were a bad thing. Now Republican voters' opinions of free trade are at their lowest since 2009, when Pew began asking this question.

It's not just Republicans who are struggling with trade in this populist election.

During the presidential primaries, Hillary Clinton had her own moment of reckoning when she decided during the presidential primaries that the TPP — the deal she advocated for while secretary of state — wasn't good enough for her to support now. That, of course, was a reflection of how unpopular free trade is with her base. And Thursday's Pew survey suggests Clinton has less skeptical voters than Trump does: 58 percent of Democrats and Democratic-leaning registered voters think free trade has been a good thing.

For better or worse, Trump appears to be changing how his party talks about free trade deals — specifically, the one Obama wants the Republican-controlled Congress to pass this year. And that's the weirdest thing of all about this new anti-trade movement in the Republican Party:

3) Senate Republicans who don't agree with Trump may have no choice but to agree with Trump. Holding TPP at arm's length puts these Senate Republicans more in line with the nominee many are also so desperately trying to keep at arm's length, too. It's yet another example of how Trump is changing the Republican Party, whether they like it or not.