The Trump campaign is currently spending $5.4 million per week on Facebook ads, almost assuredly making it the platform's largest advertiser

I don't know about leadership. According to Wikipedia, Zuckerberg has never revealed his political views. But the money still goes to pay the salaries of the rank and file. In that sense it's flowing to mostly Democrats. Also, Facebook is in Silicon Valley which has a heavy tilt towards Democrats, so at headquarters they probably buy services from mostly Democrats, and they pay California taxes to a government controlled by Democrats.

As policy, Facebook is trying to be nonpartisan. This is a common corporate policy since it doesn't make business sense to alienate half your customers. Also, companies and their PACs regularly give money to both sides so they can get politicians on the phone whoever is in office. But maintaining official neutrality when your employees increasingly don't see things that way gets increasingly difficult.

You might be thinking of this Washington Post story. However, the "political shift" it talks about is appeasing Republicans.

“Facebook does not speak Republican,” said a former employee of Facebook’s Integrity Team, which was created to ensure safety and trust on the platform, who spoke on the condition of anonymity to speak freely about a former employer. “This is what they know about Republicans: Tell them ‘yes’ or they will hurt us.”

That is, Republicans are "them," not "us," from most tech employees' point of view.

Although, apparently this isn't working all that well. The big tech companies have few friends in Washington these days.