(CNN) Following President Donald Trump's racist tweets this weekend telling "'Progressive' Democrat Congresswomen [to...] go back and help fix the totally broken and crime infested places from which they came," only a small number of Republican members of Congress have been willing to critique Trump .

It would be easy to say the minimal response from Republican lawmakers is because they don't go after Trump in general. But that ignores Republicans who vocally disagree with him on trade , for example.

We can peg Republican silence (for the most part) on the fact that many Republicans who might be willing to go after Trump on issues related to immigration are no longer in Congress. They either retired, died or were beaten in the 2018 midterm elections.

Last year, I looked at a group of 23 of the most pro-immigration House Republicans. These were lawmakers "who signed onto a discharge position to force a vote on a bill that would have created a [Deferred Action for Childhood Arrivals program] fix," after Trump terminated DACA through an executive order and asked Congress to act.

Of this group of 23, 14 (61%) are no longer in the House, including Carlos Curbelo and Ileana Ros-Lehtinen. Of those nine remaining, a number have come out against the President . Rep. Will Hurd of Texas called Trump's tweet "racist." Rep. John Katko of New York said, "The President's tweets were wrong." Another, Rep. Fred Upton of Michigan, said he was "appalled by the President's tweets."

Outside of this group, a low percentage of Republicans commented on the President's tweets. One of the few was Rep. Mike Turner of Ohio, who said they were "racist." Turner, like many of that group of 23, has a history of taking more moderate positions on immigration.

We can see how Turner's record stacks up by looking at the voting score card of NumbersUSA , a hardline immigration group that advocates "for lower immigration levels." The most hawkish Republicans on immigration get A+'s, while those who are in favor of immigration reforms like DACA get F's.

Turner has earned a C- over his career and a D+ over the last two congresses. That's far higher than the average B+ among the Republicans who served last Congress and won reelection.

Indeed, Turner's record is closer to those Republicans in 2018 whose seats are now held by Democrats. Among that group, their average score was a C+. Additionally, eight of the 16 who had a D or worse are no longer serving.

In other words, the House lost a lot of moderate Republican voices on immigration.

We see basically the same pattern when we expand our analysis to the Senate. The elected Republican senators who stepped down, died or were defeated in 2018 tended to be more moderate on immigration. Sens. Thad Cochran of Mississippi (C+), Bob Corker of Tennessee (C+), Jeff Flake of Arizona (C-), Orrin Hatch of Utah (C), Dean Heller of Nevada (C) and John McCain of Arizona (D) were all below the average Republican senator's score of a B.

Now, you can obviously critique Trump's tweets, even if you are hawkish on immigration. Rep. Pete Olson of Texas did so

For Trump critics, there is a bright side to a lack of moderate Republican voices on immigration: Those who have left the House have been replaced by Democrats. Democrats are more than willing to call Trump out and try to pass a resolution condemning him for his weekend tweets.

CORRECTION: This story has been updated to reflect that Rep. Mike Turner has taken moderate immigration positions.