President Trump took to Twitter on Monday to claim his predecessor’s administration launched an investigation into his campaign with “zero proof of wrongdoing” to help Hillary Clinton win — a scandal “bigger than Watergate.”

“Why did the Obama Administration start an investigation into the Trump Campaign (with zero proof of wrongdoing) long before the Election in November? Wanted to discredit so Crooked H would win. Unprecedented. Bigger than Watergate! Plus, Obama did NOTHING about Russian meddling,” the president wrote on the messaging site.

The FBI launched an investigation into the Trump campaign in July 2016, former agency director James Comey testified to a House committee, to follow up on leads that Trump associates were in contact with Russian officials.

The Justice Department also received warrants from a federal surveillance court to monitor Carter Page, a former Trump campaign aide — a move that has led Democrats and Republicans to release competing memos about the process.

Trump has attacked former President Barack Obama before for not taking a firmer stand on Russian election meddling.

But former members of the Obama administration said they were leery about going public with Moscow’s meddling in the months leading up to the 2016 election for fear of making it look like they were trying to sway it to Clinton.