President Donald Trump and top House Republicans are ramping up a sweeping investigation into former President Joe Biden’s use of a mechanical signature device known as the autopen, raising questions about the legitimacy of executive actions taken during Biden’s presidency — especially a wave of last-minute pardons signed with the device.

While House Republicans and Trump appear to be aligned in their desire to investigate Biden’s fitness to serve, there is some frustration brewing among congressional committees about how quickly the Trump administration is responding to some of their requests, according to multiple GOP congressional sources familiar with the matter.

Trump speculated on Tuesday that legislation had been signed via autopen during Biden's presidency. What is an autopen? Here's what to know.