House Democrats, with their new majority, will have an expansive new toolkit once they take control of the chamber on Jan. 3 to protect special counsel Robert S. Mueller III’s investigation — even if acting Attorney General Matthew Whitaker decides to shut it down.

If President Donald Trump, through Whitaker or his full-time replacement, does indeed order Mueller to shutter his investigation into Russia’s interference in the 2016 U.S. election, that would trigger a quick response from Democrats. In two months, they will wield the all-important power of subpoenaing officials.

Democrats’ first step would be to preserve evidence Mueller has collected over roughly the last year and a half so that the Trump administration doesn’t confiscate files and hide them.

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