"Mueller has already brought New York's ambitious AG Eric Schneiderman into the investigation of the finances of former Trump Campaign Chairman Paul Manafort, possibly in part to immunize against a presidential pardon."

Attorneys general are well known as a group of very politically ambitious officials. Nine senators formerly served as attorney general, as did seven sitting governors, two current cabinet members and one former president, Bill Clinton. Numerous other officials have served as district attorneys before stepping up to higher office.

The crusading lawyer has been a popular political figure for centuries, and presidents dating back to John Adams gained fame in the courtroom before winning office. The attorneys general do not actually deal with headline grabbing violent prosecution – their real role is acting as the state's civil attorney – but in recent years they have been sure to get involved whenever they can against industries.

The AGs took the lead against the tobacco industry and in New York, Elliot Spitzer grabbed the title of the "Sheriff of Wall Street" before his ill-fated turn as Governor. On the Republican side of the aisle, AGs led the legal fight against Obamacare and against federal environmental regulations. Former Oklahoma Attorney General Scott Pruitt was so active in this regard that Trump appointed him the EPA Administrator.

For the current group of attorneys general, there is good reason to think that a hard-hitting investigation of Trump could help their own political careers. Both of New York's last attorneys general moved up to the Governor's mansion, and an investigation into the Trump team will only help Schneiderman as he looks to follow his predecessors.

States like Florida, where the term-limited AG has been a staunch Trump ally and was herself the subject of controversy for squashing an investigation into Trump University, will be facing elections for AG in 2018. Candidates for the AG job may quickly discover that promises of an investigation into Trump's campaign and his related businesses are potential popular issue in the Democratic primary and beyond.

Trump has recently exercised his pardon power for the first time in Arizona, pardoning Maricopa County Sheriff Joe Arpaio from a potential criminal conviction. Trump may now feel that this test shows that using the pardon can help him fulfill his previous trial balloon and stave off a wider-ranging investigation of his campaign.

But the limits of his "complete power" stop at the border of the federal-state power divide. With at least one attorney general – if not many others – seeing the benefit of a taking Trump on in an investigation, a pardon may not be the red light that he thinks. It may instead be a starting gun for state officials to begin their own work.

Commentary by Joshua Spivak, a senior fellow at the Hugh L. Carey Institute for Government Reform at Wagner College in New York. He blogs at The Recall Elections Blog. Follow him on Twitter @recallelections.

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