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CNN  — 

While President Donald Trump was busy rhetorically destroying America’s neighbor to the north and disrupting the broader G7 conference over the weekend, you could have heard a pin drop among congressional Republicans.

And while the President was in Singapore meeting with North Korean leader Kim Jong Un – a meeting that Republicans had decried when then-President Barack Obama said he would be open to sitting down with Kim – the response from the bulk of Republicans back home was largely celebratory.

Why so quiet and respectful? Two names: Martha Roby and Mark Sanford.

Those are Republican members of Congress from Alabama and South Carolina, respectively. And both have been on-again, off-again critics of aspects of Trump’s behavior and approach, both as a candidate and while in office. And both seem to be paying a political price for that willingness to criticize the President. Roby was forced into a runoff earlier this month with a Republican who cast her as insufficiently loyal to Trump. And now Sanford, a South Carolina Republican in the House, faces a serious primary challenge in his Charleston-area House seat from a state legislator portraying him as – wait for it – insufficiently loyal to Trump.

“[Sanford] talks about working with President Trump on the border wall,” says opponent Katie Arrington in one campaign ad. “He was one of only five Republicans who refused to support our President and voted against Trump’s border wall. We’ve all seen Mark on TV attacking our President. Who does he think he’s fooling?”

Trump endorsed Arrington in a blistering tweet on Tuesday afternoon, accusing Sanford of being “unhelpful.”

“Mark Sanford has been very unhelpful to me in my campaign to MAGA,” he wrote. “He is MIA and nothing but trouble. He is better off in Argentina. I fully endorse Katie Arrington for Congress in SC, a state I love. She is tough on crime and will continue our fight to lower taxes. VOTE Katie!”

This, from CNN’s own Harry Enten, captures why breaking with Trump in any real way creates real political peril for a GOP incumbent:

The problem that Trump’s Republican adversaries are learning is that it’s not 2016 anymore. Even as Trump was winning the presidential election, his net favorability (favorable-unfavorable) rating among Republicans in an average of polls was just +50 points. That’s far short of the maximum +100 point rating. You could, in other words, oppose or critique Trump as a Republican (as Sanford did in 2016) and not get chased out of the party.

“Today, it’s totally different. Trump’s net favorability among Republicans is up to +71 percentage points on average. There are very few Republicans who disagree with Trump. Trump’s approval rating (a slightly different measure than favorable rating) stands at 87% in the latest Gallup poll. To put that in perspective, only two other presidents since 1950 have had higher approval ratings among their own party heading into a potential presidential primary.”

(Side note: Harry’s point above is why no one should take the idea of Trump losing in a Republican primary fight in 2020 all that seriously.)

Donald Trump is the Republican Party now. Or at the very least, he is the Republican Party base. And that base is who votes in typically low turnout primaries.

Politicians, contrary to prevailing wisdom, are not, by and large, dumb. And that’s especially true when it comes to their own self-preservation.

So imagine you are a Republican politician with a safe seat in Congress who doesn’t agree with Trump on trade – or the way he conducts himself more broadly on the national and international stage.

Do you:

a) Speak out against Trump where you disagree so voters know where you stand?

OR

b) Keep your disagreements with Trump private?

The answer for 99.9% of Republicans in office at the moment is “B.” Because “A” has no reward or even the potential of a reward. If you want to keep your seat, disagreeing publicly with Trump is the surest way to lose it. Sure, some number of constituents might condemn your silence on Trump’s transgressions, but were they going to vote for you anyway? And are there enough of them to tip any sort of election?

In an impassioned speech on the Senate floor, Tennessee Republican Sen. Bob Corker on Tuesday accused his party of being afraid to stand up to Trump.

“We might poke the bear!” said Corker, who is retiring at the end of his term. “My gosh, if the President gets upset with us we might not be in the majority,” he said sarcastically, referring to sentiments he often hears from colleagues.

Politicians tend to do what is easy and what it makes it most likely that they keep their jobs. (They’re just like us!) And, at the moment, that is offering unwavering support for Trump.

No one wants to be the next Jeff Flake, Roby or Sanford.

CNN’s Saba Hamedy contributed to this report.