Why is the lineup of prospective GOP presidential candidates beginning to look like, well, a lineup?

Chris Christie went to campaign this week for Wisconsin Gov. Scott Walker, putting the New Jersey governor in the company of a man who is in almost as much legal jeopardy as he is. Between them, the two would-be 2016 presidential nominees are the subjects of six investigations.

But Texas Gov. Rick Perry, another presidential aspirant, is far ahead of them in the mug-shot primary: He’s already under indictment on two felony counts related to abuse of power. And, speaking of felonies, former Virginia governor Bob McDonnell, long considered presidential timber, was convicted on 11 corruption counts after his salacious trial this summer that disgraced him and his wife.

Democrats are trying to tie another prospective presidential candidate, Ohio Gov. John Kasich, to a Republican contributor who was convicted this summer of witness tampering in a campaign-finance case; the governor had been subpoenaed to appear in the case but was never called.

Beyond that, the Republican governors of Iowa, Kansas, Georgia, Pennsylvania, Maine, South Carolina and New Mexico all face varying degrees of legal liability on matters ranging from influence peddling to the firing of whistleblowers. Completing the GOP version of a most-wanted list: John Rowland, the former governor of Connecticut, who was found guilty last month of conspiracy charges in a campaign-finance case. It was the second time he had been convicted on criminal charges.

Lest Democrats celebrate their rivals’ legal woes too much, they should recall that federal prosecutors are probing New York Gov. Andrew Cuomo (D) over his shutdown of an anti-corruption commission, and federal prosecutors and Illinois lawmakers are investigating the activities of Gov. Pat Quinn’s (D) administration. Republicans point to eight other states where Democratic administrations or Democratic gubernatorial candidates have some exposure to lower-profile legal or ethical scrapes.

There hasn’t been this much corruption around the table at the National Governors Association since Rod Blagojevich dined alone.

This doesn’t necessarily mean governors, or other politicians, are more corrupt than they used to be; there has always been some sense of entitlement among elected leaders, a belief that the usual rules don’t apply to them. Melanie Sloan, executive director of Citizens for Responsibility and Ethics in Washington, adds that “unfathomable amounts of money flowing through the system” have increased the opportunity for misconduct, while the proliferation of media and electronic paper trails makes it more likely to get caught.

To Sloan’s list, I’d add one more: the criminalization of politics that has become routine since Bill Clinton’s impeachment. That case, in which a president was impeached by the House and tried by the Senate for what was essentially a personal indiscretion dressed up as a perjury and obstruction case, created new norms: Politicians decided they could use legal means to settle political disputes. If you can’t beat your opponent at the polls, take him out in court.

Both sides play this way, but there’s some rough justice that Republicans, who popularized this criminalization of politics in the 1990s, now find at least three of their top presidential prospects being hoist with the GOP’s own petard.

New Jersey’s Christie, of course, has Bridgegate and related troubles. The campaign of Wisconsin’s Walker is being investigated over allegedly illegal campaign finance coordinated with various conservative groups; a federal appeals panel ruled last month that prosecutors could proceed with the long-stalled investigation. Then there’s Perry, who demanded the resignation of a Democratic district attorney after she was caught driving drunk. When she refused, he vetoed funding for her public-integrity unit, which prosecutes official corruption. Now a grand jury has indicted Perry on charges carrying up to 109 years in prison combined.

There’s reason to believe all three prospective presidential candidates acted badly. But that’s not always illegal. Just this week, the highest criminal court in Texas agreed to throw out money-laundering and conspiracy charges against Tom DeLay, the former House Republican leader. DeLay had abused power in all kinds of ways — his shakedowns of donors and his asking federal authorities to track an airplane carrying Texas Democratic legislators comes to mind — but in the eyes of the law he is now without taint.

DeLay is now talking about a comeback in Washington, but he should be warned: A clean record may disqualify him from the Republican presidential ballot in 2016.

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