Ever since President Donald Trump retook office for his second term, some of his supporters have been pushing for his likeness to be added to the iconic Mount Rushmore monument. Most prominently, one of his supporters in Congress, Rep. Anna Paulina Luna, introduced a bill to do just that. Yet even though the legislation has not advanced in the Capitol, that isn’t the largest issue the bill is facing. Even if the measure passed, there is not enough suitable rock on the mountain to carve Trump’s, or anyone else’s, face on the mountain.

“It comes down to the geology, the engineering,” said Paul Nelson, a retired engineer who oversaw the rock monitoring system at Mount Rushmore. “It just can’t be done.”

The stone’s limitations have been known for a long time, as early as May of 1936, when the lead sculptor of the monument— Gutzon Borglum—wrote that the “stone limitations are so serious that I doubt if it would be possible to change the composition, which is fixed, in any way to include a fifth head.”

However, that has not stopped supporters of Trump from floating the idea of his head on the monument. In fact, Interior Secretary Doug Burgum told Lara Trump, Donald Trump’s daughter-in-law, “There is certainly room for it,” on her Fox News show when asked if Trump could be on Mount Rushmore.

Yet, Trump is not the first president to have his supporters want his head on the mountain.  With efforts being made to add Ronald Reagan after his death in 2004, as well as efforts before the mountain was even complete by first lady Eleanor Roosevelt to add suffragist Susan B. Anthony.

But Dan Wenk, who was the superintendent at Mount Rushmore for over a decade, has quickly shut those hopes down, saying, “It’s a wonderful thing to speculate about who could or should be on Mount Rushmore, but it can’t be done.” And comparing adding another head to the mountain to adding another figure to Da Vinci’s “The Last Supper.”

Wenk added that, while it may look like there is space next to Lincoln or Washington, the rock is “not suitable for carving,” as it is “very fractured, it’s very soft.” Regardless of public opinion and beliefs about whether any new president should or should not be added, Wenk emphasized that “at the end of the day, it can’t be done. It doesn’t matter how worthy someone is—if the rock is not there, you can’t carve them.”