LOUISVILLE, KENTUCKY - NOVEMBER 5: Soon to be the Senate Majority Leader of the US Senate after winning the Kentucky Senate race and the GOP winning a majority of seats in the US Senate, Senate Minority Leader Mitch McConnell leaves a press conference with national and local media at the University of Louisville in Louisville, Kentucky, Wednesday, November 5, 2014. Senate Minority Leader Mitch McConnell defeated Kentucky Secretary of State Alison Lundergan Grimes to be the longest serving Senator in Kentucky history. (Photo by Melina Mara/The Washington Post via Getty Images)

WASHINGTON -- Over the past three years, House Republicans have repeatedly tried, and failed, to bar federal agencies from adopting regulations to govern the campaign finance landscape created by the Supreme Court's 2010 Citizens United decision. Now, with their party seizing control of the Senate, that effort to stop new rules may win, too.

The Senate will likely be led next year by the primary antagonist to campaign finance reformers, Sen. Mitch McConnell (R-Ky.). Over three decades, McConnell has made it a top priority to disrupt and degrade campaign finance regulations. With a firm belief that limits on campaign funds are a direct impediment to the First Amendment right of free speech, he has opposed past reform efforts, including challenging in court the 2002 McCain-Feingold law, the passage of which he once called the worst day in his political career.

With McConnell's ascendance and with Republicans increasingly unified in opposition to campaign finance reform, its advocates expect a full-frontal assault on the few areas where they had hoped to enact new rules in the post-Citizens United world.

"This has always been Senator McConnell's DNA issue," Democracy 21 President Fred Wertheimer said, "the issue he seems to care most about."

In an interview with The Huffington Post, Wertheimer, the dean of campaign finance reformers in Washington, predicted in particular that Republicans will seek to defund efforts by the Internal Revenue Service to write new regulations governing the political activity of certain nonprofits.

"Our assumption is we're going to have to fight these kinds of battles over the next two years," he said.

That concern does not come out of the blue. House Republicans attached a rider to appropriations legislation to prevent President Barack Obama from issuing an executive order mandating disclosure of political contributions by federal contractors. The rider was prompted by a conservative website's reporting on a leaked draft of that order. The rider eventually passed a part of appropriations legislation.

Those who vocally oppose campaign finance regulations were also instrumental in helping the GOP win back control of the Senate. The U.S. Chamber of Commerce spent more than $35 million to support Republicans. The Koch brothers' groups reported at least $26 million in spending to the Federal Election Commission, but dished out an additional $50 million-plus on issue ads to support Republicans early in the election cycle.

The main object of Wertheimer's concern is a rider aimed at the IRS that House Republicans tried to add to appropriations legislation in 2013 and 2014. The measure would prevent the tax agency from spending any funds on writing or enforcing new rules to rein in political spending by tax-exempt nonprofit groups.

In 2013, the IRS admitted to improperly targeting a number of political groups, including those with the words "tea party" or "patriot" in their names. Congressional Republicans insisted this showed that the Obama administration was targeting political opponents. Democrats and campaign finance reformers responded that it was indicative of the IRS' vague and out-of-date rules on how to approve tax-exempt status and judge political and campaign activity.

"Now more than ever, we need to send a clear message to the Obama administration that the First Amendment is non-negotiable, and that apologies after an election year are not a sufficient response to what we now know took place at the IRS," McConnell said in a speech at the outset of the scandal.

After a host of congressional hearings, firings and suspensions, the IRS announced a rulemaking procedure to write new regulations covering both the way it undertakes the approval and review of tax-exempt status and the means by which it judges whether a tax-exempt group has spent an inappropriate amount of time electioneering. This rulemaking was decried by Republican opponents and hailed by Wertheimer, who then dropped a prior lawsuit over the agency's purported lack of enforcement of political activity rules.

Republican leaders, including McConnell and House Speaker John Boehner (R-Ohio), wrote to interim IRS Commissioner John Koskinen, "It is our view that finalizing this proposed rule would make intimidation and harassment of the administration's political opponents the official policy of the IRS and would allow the Obama administration to use your agency as a partisan tool."

It was during this period that House Republicans pushed the rider that would deny funding to enact these regulations.

If Congress moves to block new IRS rules on nonprofits' political spending through a rider or other means, Wertheimer said he will fight it. "This is open and shut that the [current] regulations do not comply with the law," he said. "If Congress blocks this, we will bring our lawsuit again."

But Wertheimer is not focused only on the fate of potential IRS regulations. Since 2011, Republicans have also introduced legislation and attempted to attach spending-bill riders to gut the ability of other agencies -- including the Federal Communications Commission and the Securities and Exchange Commission -- to write rules on campaign funding and spending. Even when the Republican measures didn't pass, the threat was felt.

In 2012, House Republicans attached a rider to an appropriations bill to deny the FCC funding to require online disclosure by broadcast TV stations of their political advertising files. That rule was strongly opposed by the National Association of Broadcasters and the Chamber of Commerce. The bill to which the rider was attached did not pass, but Wertheimer warned the rider could come back now.

Reform groups have also put pressure on the FCC to require television stations to disclose "the real sponsor" of ads put forward by innocuous-sounding groups. The FCC has rejected this idea so far, but the reformers don't want Congress to cut off any future discussion.

In 2013, with the SEC under pressure to write political disclosure regulations for publicly traded companies, House Republicans introduced legislation to prevent the commission from spending money to enforce such rules. The SEC has since backed away from issuing those regulations, and Republicans have similarly not pursued related riders.

Next year, the House GOP will have a much more powerful ally against campaign finance reform in the Senate. If Republicans go ahead and push these and similar funding restrictions, Wertheimer urges Obama and Senate Democrats to oppose them.