Iowa Republican Sen. Chuck Grassley issued his own fact-check of President Trump Thursday, challenging his claims that his planned tax cut would be the biggest in U.S. history.

In fact, Grassley claimed, the Bush tax cuts that he helped pass in 2001 were bigger.

Adjusted for inflation, the former Senate Finance Chairman claimed, the 2001 tax bill was a $1.87 trillion cut.

Currently, the Senate is working toward a budget that would limit Trump's tax cuts to $1.5 trillion, athough that could be changed.

On Wednesday, Trump boasted at the White House that "I'm giving the largest tax cuts in the history of this country. In addition to that, there will be reform."

Although Grassley challenged the premise of Trump's claim, he commended him for the tax reform effort, saying that the tax framework "sets out badly needed cuts."