Who told VOA news that no president has ever tried to pardon himself?

Choices:
A. Susan Low Bloch of Georgetown University
B. Press Secretary Sarah Sanders
C. Keith Whittington of Princeton
D. not enough information
Susan Low Bloch of Georgetown University
WHITE HOUSE — President Donald Trump on Monday declared he has an "absolute right" to pardon himself and then also tweeted his assertion that the federal government investigation into ties between his 2016 election campaign and Russia is "totally unconstitutional."
While Trump has frequently ignored established norms and challenged the understood limits of presidential powers, his latest comments are viewed by some legal scholars as unprecedented and testing constitutional boundaries.
"I was shocked" by Trump’s tweets, said Susan Low Bloch, a law professor at Georgetown University.
"No president has ever tried it," she told VOA News. "It’s unlikely the president can pardon himself. I think the court would say no" and if he did give himself a pardon, "most congresses would impeach him."
Bloch also notes when most people accept a pardon "it’s an admission of guilt," thus it would be a bad idea for Trump to pursue such a course of action.
The professor, who has testified before the Senate on whether a president can be indicted and tried while in office, says the special counsel is "absolutely constitutional."
Another constitutional scholar, Keith Whittington at Princeton University, said, "I think it is important to note that the president’s comments reference serious arguments that are being debated by legal scholars, but these are difficult and unusual constitutional questions that would ultimately be answered in the courts."
According to Northwestern University Law Professor Andrew Koppelman, "Trump's position on pardons is consistent with the Constitution's text, but inconsistent with the overall structure. It means that the President could commit capital treason, or any other federal crime, and then immediately pardon himself.
"It means that he could commit murder in the White House," Koppelman said. "It makes no sense within the Constitution as a whole."
Asked by reporters Monday about Trump’s comment on his ability to pardon himself, White House Press Secretary Sarah Sanders repeatedly replied: "The president hasn’t done anything wrong."
Whittington, a professor of politics, told VOA News, "The courts have recognized some implicit limits on the pardoning power in the past and they would have to assess whether a self-pardon is legally valid or falls outside the scope of the pardoning power. It is not obvious how the courts might respond to such an unusual pardon."