(CNN) President Donald Trump is not afraid to take credit when things go right. He's repeatedly crowed about the stock market -- which has been way up! -- and he's taken personal credit, amazingly, for a lack of airline deaths .

We have documented, in particular, now that stock market gains are not entirely attributable to him and the lack of airplane deaths is even harder to give credit for.

But what about when things go horribly wrong?

If Trump is going to take full credit for no planes crashing and for years of seemingly uninterrupted stock market gains, should he get immediate blame for the largest one-day stock market plunge (as measured by points) in history? What about a string of four deadly train crashes. If he gets credit for no planes crashing, should he accept blame for the trains?

You normally wouldn't think of the comparison, except for the fact that he has invited it.

Here's what he said in January about the lack of plane deaths : "Since taking office I have been very strict on Commercial Aviation. Good news -- it was just reported that there were Zero deaths in 2017, the best and safest year on record!"

There actually haven't been any US commercial airline deaths for nine years. So his administration and nearly all of his predecessors get that seal.

In terms of train deaths, Trump has so far been silent, although he has repeatedly promised to make improving US infrastructure a priority. During the State of the Union address, the President said he'd to spend $1.5 trillion on it -- a number that made some Republicans blanch. He has not said how his administration would pay for the improvements and further, he hasn't said what, if any, of that money would go to improving train safety, which you could reasonably pull from infrastructure funding.

Of the four recent Amtrak crashes, two involved other people -- such as the truck that a train carrying GOP congressmen in Virginia struck -- on the tracks. No real blame for Trump there.

But there is an opportunity for the government to institute positive train control systems on trains. That effort, which began long before Trump took office, has lagged during both the Trump and Obama administrations even though it could feasibly have avoided two of the crashes.

Here's a summary of that issue with a lot of reporting from CNN's Gregory Wallace and Rene Marsh: Positive Train Control, or PTC, is intended to prevent crashes like two of the recent Amtrak incidents, the derailment in Washington State and this weekend's collision in South Carolina.

What is PTC?

It's a system that combines GPS, wireless radio and computers to monitor trains and stop them from colliding, derailing or speeding, per previous CNN reporting . If a train isn't being operated in accordance with signals, speed limits or other rules, the system will slow or stop it. Imagine what would happen, the National Transportation Safety Board said in a fact sheet, if an engineer suffering from a cold didn't notice a red signal and failed to stop the train?

"With PTC, the train stops anyway," the National Transportation Safety Board said. "Without PTC, real world results have been tragic. ... Without it, everybody on a train is one human error away from an accident."

Description from the Federal Railroad Administration : Positive Train Control uses communication-based/processor-based train control technology that provides a system capable of reliably and functionally preventing train-to-train collisions, overspeed derailments, incursions into established work zone limits and the movement of a train through a main line switch in the wrong position.

For Positive Train Control to work, it must be installed on the rail line AND the trains using those rails.

What the law says

Congress acted within weeks of a deadly 2008 crash : A commuter train, whose operator had been texting, slammed into a freight train outside Los Angeles. The commuter train had not braked before the crash.

2015, 2018 and 2020 deadlines : The Positive Train Control Enforcement and Implementation Act of 2008 required Positive Train Control be installed by December 2015. As that deadline approached, Congress extended it to December 31, 2018, "with the possibility of an extension to a date no later than December 31, 2020, if a railroad completes certain statutory requirements that are necessary to obtain an extension."

Where PTC is required -- per the Federal Railroad Administration: In 2008, Congress required Class I railroad main lines handling poisonous inhalation-hazard materials and any railroad main lines with regularly scheduled intercity and commuter rail passenger service to fully implement Positive Train Control by December 31, 2015.

So what's the delay?

It's expensive.

"The real dilemma that you face ... is you have a limited, a finite amount of money each year that you can spend on infrastructure and safety," Peter Goelz, a former managing director of the National Transportation Safety Board told CNN's Catherine Shoichet in 2015

"Do you spend the money on high consequence, low probability events? And I would call the accident two days ago high consequence but low probability. Or do you spend it on high probability, lower consequence items such as working on electrical systems or air conditioning?" Goelz said.

Amtrak progress : Amtrak has equipped 49% of its locomotives and 67% of its tracks with Positive Train Control, according to Federal Railroad Administration data from the second quarter of 2017.

Amtrak caveat : While Amtrak has some of its own tracks, such as in the Northeast Corridor, about 70% of the miles traveled by Amtrak trains are on tracks owned by freight railroads.

What is the Trump administration doing?

Early reports are indicating that that fatal Amtrak derailment out in Washington -- similar to the 2015 derailment in Philadelphia -- could have been prevented by positive train control, which Congress back in 2008 mandated was supposed to be on all lines by 2015. That's been pushed back and it's only one quarter of passenger lines right now. Is this White House considering any steps to speed up the implementation of positive train control to stop these kinds of accidents?

"Right now we're continuing to review and investigate exactly what took place yesterday," said White House press secretary Sarah Sanders said on December 19, the day after the Washington crash. "And once we have more detailed determination on that, we can take steps to prevent things like this from happening in the future."

But Transportation Secretary Elaine Chao wrote to railroads earlier this year reminding them of the deadline.

The bottom line is this is a complicated and expensive issue -- and one the White House and Trump are not going to want to focus on, unlike a feelgood story, like no airline deaths. It would be as problematic to blame him for train deaths as it would be to give him full credit for no plane deaths.