This sentence has poor grammar in many ways.
I would change the start to:
"I think it's important to understand, that's precisely..."
Next, if we're saying "the reason", it would be better as "the reason why..."
If we're saying "by which", it would be better as "the reasoning by which..."
We can also say "the logic with which..." or "the rationale via which..." or "the end goal for which..."
Also, "the president" doesn't need capitalising. The capitalisation is only needed when you're naming him, such as "the reason why President Bush..."