WASHINGTON (AP) — It’s one thing to be Montana’s lieutenant governor. It’s another to be a U.S. Senate candidate in one of the states that will determine which party controls that 100-member chamber.

As Sen. John Walsh of Montana learned this week, one difference is the huge amount of resources poured into “opposition research,” to flyspeck a candidate’s history of comments, business dealings, legal actions, romances, health, writings and countless other items in search of a flaw that might cripple his or her campaign.

Walsh, a Democrat, wasn’t universally known even in Montana when he became lieutenant governor in 2013. He was obscure nationally when he was appointed last February to fill the Senate seat vacated by six-term Democrat Max Baucus.

On Thursday, however, he found his name and photo on the front page of the New York Times, plus several Montana newspapers, and not in a helpful way. The Times reported that much of Walsh’s 2007 master’s thesis was lifted from other publications without adequate credit, which is considered a serious academic offense.

Walsh partly blamed the insufficient attribution on post-traumatic stress disorder from his time in combat in Iraq.

The Times did not say how it obtained the story. But it looked like the product of classic opposition research: An obscure document suddenly surfacing in politically damaging circumstances.

Montana Gov. Steve Bullock placed Walsh in the open Senate seat in part to give him a running start in what everyone agreed would be tough campaign this fall against GOP Rep. Steve Daines. President Barack Obama lost Montana by 13 percentage points, and Republicans have been itching to grab the Senate post once the deeply entrenched Baucus left it.

Republicans have to gain six net Senate seats this fall to control the chamber.

Moving Walsh from Helena to Washington put him in the crosshairs of the GOP research machine, which would be likely to scrutinize a candidate’s academic papers, plus countless other things.

Tim Miller of America Rising, the Republicans’ chief political research group, declined to say whether his organization played a role in unmasking Walsh’s apparent plagiarism. But after Republicans failed to take over the Senate in the last two elections — partly because of poorly vetted and unprepared candidates — the party has worked hard “to professionalize opposition research and tracking, and bring a more thorough and intense operation to bear,” Miller said. Tracking involves campaign workers videotaping nearly all public appearances by the other party’s candidate.

A 2008 study by the non-profit Center for Public Integrity said opposition researchers “are widely considered the lowest form of life in the campaign business. Their work happens below the radar screen,” and it’s “what usually makes or breaks a candidate for the White House.”

Expensive, high-quality “oppo-research” is now more prevalent in key Senate races — and some House and gubernatorial races — thanks to millions of dollars pouring into Democratic and Republican coffers from groups raising unlimited sums from people who want to influence the government.

Computer software makes it easier for anyone, including colleges, to detect plagiarism. Veterans of opposition research say a candidate’s academic papers are likely targets for scrutiny, although higher priorities might include impolitic remarks, legal or financial problems, and sex scandals.

These research experts say the first thing a sophisticated campaign does is scrutinize its own candidate. It wants to discover any embarrassing details before opponents do, and decide how to handle them.

“It’s important for a campaign to know everything they can, not only about their opponent, but also about their own candidate,” said Rodell Mollineau, former head of the Democratic research group American Bridge.

Top Democrats in Washington said a self-examination process may have begun when Walsh declared last October he would run for Baucus’ seat. But things suddenly sped up when Baucus left the Senate in February, allowing Bullock to appoint a fill-in to serve until this fall’s elections.

Increasingly, opposition research is used in intra-party battles, as establishment Republicans try to week out insurgent primary challengers who might not appeal to mainstream voters in the fall.

Tea party favorite Matt Bevin was bedeviled by repeated revelations in his ultimately doomed effort to deny Sen. Mitch McConnell the GOP nomination in Kentucky this year. For instance, after Bevin criticized the 2008 federal bank bailout, reporters were pointed to documents from a Bevin-led investment fund that had highly praised the bailout.