Often accused of bringing a knife to a gunfight, Democrats are finally matching Republicans for cunning in the US midterms -- but their new embrace of the political dark arts is proving divisive.

With both sides choosing candidates for the next Congress, the party of President Joe Biden has been wading into Republican contests across the nation to help extremist candidates and hurt moderates.

In swing states from Arizona to Michigan, Democrats have poured tens of millions of dollars into TV ads calculated to boost Republican conspiracy theorists who deny that Biden won in 2020, as well as anti-abortion hardliners.

The bet is that, come November, voters will recoil from the radicals -- often backed by former president Donald Trump -- in favor of Democrats who look much more reasonable by comparison.

Many partisans have voiced relief that the party is finally showing some of the guile that has enabled Republicans to bend protocol on Senate voting rules and Supreme Court nominations.

But analysts and prominent voices within the party's own ranks are warning that while manipulating the process to get more beatable opponents may look like smart politics, Democrats are playing with fire.

"Burning down villages in the name of saving them tends to leave only ashes," Peter Loge, director of the Project on Ethics in Political Communication, based at George Washington University, told AFP.

"Meddling in opposing party primaries by raising policy issues can be strategically clever... But amplifying lies about elections, promoting baseless conspiracies, and giving airtime to attacks on democratic institutions is wrong."

'By the people'

In the Michigan primary, Trump-backed election conspiracy theorist John Gibbs narrowly pipped Peter Meijer, one of 10 House Republicans who voted to impeach Trump over the 2021 insurrection.

Gibbs can thank the Democratic Congressional Campaign Committee for spending half a million dollars effectively promoting the former missionary, who has spread a conspiracy theory about Democrats and satanic rituals.

In the guise of attacking Gibbs, its TV spot archly claimed Gibbs was "too" conservative -- using language much more likely to be taken as a commendation than a warning by much of Trump's base.

Democrats also spent big on election deniers in Pennsylvania, Maryland and Arizona, while in Illinois Governor J.B. Pritzker and the Democratic Governors Association are reported to have parted with a staggering $35 million.

The strategy comes with obvious pitfalls, and Democrats from former White House aide David Axelrod to lawmakers Stephanie Murphy, Pramila Jayapal and Jason Crow have spoken out against it.

Dan McMillan, who heads the Save Democracy in America non-profit, believes that claiming to protect democracy while throwing fortunes at election conspiracy theorists is "big money at its worst."

"Having for decades listened to their donors and ignored the voters, politicians of both parties forgot that government by the people is what this country is supposed to stand for," he told AFP.

"They manipulate the voters instead of listening to them. Disgusting."

'Hardball politics'

Liberals helping unserious right-wingers into Congress also risks undercutting the credibility of the Democratic-led panel probing the US Capitol assault, whose members often warn of the danger Trumpists pose to democracy.

Some Democrats and independent analysts have dismissed the criticism, claiming that tougher tactics are required to highlight the extent to which the Republican Party has become radicalized.

"In a two-party system, one party is already adept at hardball politics," said Aron Solomon, chief legal analyst for lawyers' marketing agency Esquire Digital.

"It's just a disservice to the electorate not to play the same game. Being above the fray may be honorable, but today it's also a great way to be out of power for not an election but a generation."

He acknowledged however that this particular "game" could backfire, as Republicans with no moderate option in the election proper coalesce around the extreme candidates.

Veteran political campaigner Richard Gordon, an aide to 1980s and 90s New York governor Mario Cuomo, agrees that most Republican voters would back their party's candidate whoever it was.

"This will lead to more extreme candidates winning, bringing more toxicity to government, which will turn more people off... This is a dangerous and cyclical process," he told AFP.

"What the Democrats did this year, and Republican dirty tricks have done over the years, is extraordinarily dangerous and will lead to unintended consequences."

© Agence France-Presse