(CNN) Donald Trump has never been a terribly popular president. But, a series of recent polls show him in truly dangerous territory -- flirting with dipping under 40% approval just 115 days into his presidency.

The new Gallup tracking poll released Monday afternoon put Trump's job approval rating at just 38%, the lowest mark he has reached since April 1. That jibes with a new NBC-Wall Street Journal poll released Sunday that pegged Trump's job performance at 39% approval. A Quinnipiac University poll conducted before Trump fired FBI director James Comey last Tuesday showed Trump's approval at a meager 36%.

In fact, the Real Clear Politics average of all polls on Trump's approval/disapproval now stands at 40.9% approval while his disapproval sits at 53.8%.

Here's how Trump compares with the last four presidents at this exact moment of their presidencies via Gallup's amazing Presidential Job Approval Center

In the 114-117 days of their respective presidencies, Obama was at 64% approval, Bush stood at 56% and Bill Clinton was at 45%. Trump, to reiterate, is at 38%.

Why should these numbers make Republicans on the ballot in 2018 very nervous? Well, history. And, specifically this line from Gallup's Jeffrey Jones : "Since 1946, when presidents are above 50% approval, their party loses an average of 14 seats in the U.S. House in the midterm elections, compared with an average loss of 36 seats when presidents are below that mark."

Reminder: Democrats need to net 24 seats to re-take control of the US House. If they were able to do so, it would give them a very powerful check and balance against the second half of Trump's first term. It would also give them strong investigative leverage -- complete with subpoena powers -- to delve into things Trump prefers to keep hidden, like his tax returns.

But, wait, you say. The 2018 election is still 540 days away! Anything can -- and will -- happen!

Fair enough. But remember that the lower Trump goes -- and most of the available polling data cited above came before the firing of Comey and the debacle to explain why that move was made -- the harder it is to get close to 50% and the longer it will likely take.

The concern among Congressional Republicans at the moment is simmering at a low-medium level. The latest poll numbers will kick that concern up (or should).

What would set off total panic? A loss in either or both of the special House elections in Montana (May 25) or Georgia (June 20). Both are seats in what should be safe Republican territory. Defeat in either one would suggest Trump's unpopularity is a major drag downballot. And that realization would create absolute chaos among Congressional Republicans.