Fredreka Schouten

USA TODAY

WASHINGTON – Hillary Clinton may be locked in a tight battle with Bernie Sanders for the Democratic Party’s presidential nomination, but Republicans are betting she prevails and are blistering her with negative ads, mailers and calls in a precursor of what will be a costly and bitterly fought general-election campaign.

Independent groups already have reported spending nearly $4.7 million to oppose Clinton’s candidacy, vastly outpacing the $784,000 spent against Sanders, according to a tally of Federal Election Commission records by the non-partisan Campaign Finance Institute.

Several of the political groups hitting Clinton are tied to some of the biggest figures in Republican politics. Future 45, funded in part by hedge-fund billionaires Paul Singer and Ken Griffin, has spent $534,000 on ads and phone calls to oppose Clinton. Both men support Marco Rubio’s bid for the Republican presidential nomination.

American Crossroads, a super PAC affiliated with Republican strategist Karl Rove, has spent less – roughly $114,000 – but has gained attention for its provocative attacks intended to drive a wedge between Clinton and Sanders and boost the Vermont senator among the Democratic voters.

Over the weekend, Crossroads released a 30-second digital ad aimed at Hispanics and likely Democratic caucusgoers in Nevada that seeks to paint Clinton as anti-immigrant and link her to Donald Trump. Democrats caucus Saturday in Nevada, where about 17% of the electorate is Latino.

“Looking at the Democratic primary right now, we anticipate that Hillary Clinton will be the nominee,” said Crossroads spokesman Ian Prior. He said the group is working to highlight what he called Clinton’s “trust deficit” early in the campaign.

“We see it as a cost-effective way to bring up these issues when all eyes are on these primaries and caucuses,” he said.

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Clinton’s allies say the spending shows Republicans are doing all they can to avoid facing her in a general election.

"The fact that Republican special interests including hedge fund billionaires are pulling out all the stops to attack Hillary Clinton is as clear a sign as you can get that she is the candidate and future president they fear most,” Clinton spokesman Josh Schwerin said in an email.

In the face of the Republican attacks and a stronger-than-expected primary challenge from Sanders, Clinton supporters are boosting their activity.

Priorities USA Action, a pro-Clinton super PAC, has stepped up its efforts to defend Clinton, announcing late last week that it planned a $5 million push in early voting states. It’s running $500,000 in radio ads in South Carolina, ahead of the Feb. 27 Democratic primary there and is spending $4.5 million to drive early voting for Clinton among women, Latinos and African Americans in states that vote in March.

Another pro-Clinton group, Planned Parenthood Votes, on Wednesday launched a six-figure TV and digital ad campaign in Nevada featuring women who back Clinton in the state.

Bernie Sanders outraised Hillary Clinton in January

Clinton, outraised by Sanders in January, also is aggressively seeking to shore up her campaign’s finances. On Tuesday alone, she attended three high-dollar fundraising events in New York and Virginia.