WASHINGTON, D.C. - When Sherrod Brown first sought re-election six years ago, his race drew more spending from outside groups than any other Senate race in the nation, with conservative groups dropping more than $19 million in an unsuccessful bid to oust the Ohio Democrat.

So far this year, less than $1 million has been spent in that race, according to tallies compiled by the Center for Responsive Politics, which indicate the most money has gone toward contests in Alabama, Wisconsin, Missouri and Florida.

But more money will likely go into the contest between Brown and Wadsworth Republican Rep. Jim Renacci as November draws closer, if Monday's announcement from the League of Conservation Voters (LCV) Victory Fund and United Steelworkers (USW) Works is any indication.

A coalition formed by the two groups, which calls itself the New American Jobs Fund, announced what it called "an initial $3.1 million investment" to mobilize voters in Ohio, Arizona, Nevada and Montana elections whose outcomes will help decide control of the U.S. Senate.

The effort will include $500,000 in Ohio to back Brown through "persuasion and mobilization field programs" that aim to reach 58,500 voters through canvassing and direct mail in Cincinnati and surrounding Hamilton County, the group said.

"Control of the U.S. Senate is in play, and this effort will directly communicate with the tens of thousands of voters who will decide the outcome of the election in these key states," said a statement from United Steelworkers International President Leo W. Gerard. "To ensure that Congress supports the jobs and economic security our communities need, we need to elect leaders who will help build a clean energy economy that works for everyone instead of politicians who are only beholden to their corporate backers."

"We don't have to choose between good jobs and clean air and water, and that's why conservationists and labor are coming together once again to elect senators who share those values," added a statement from said LCV President Gene Karpinksi. "We know that face-to-face conversations about what's at stake bring voters to the polls, and our combined efforts will be key to retaking a pro-environment majority in the U.S. Senate that will invest in the clean energy jobs of the future and ensure that our health and safety take priority over corporate greed."

LCV Victory Fund and USW Works first partnered on voter mobilization through the New American Jobs Fund in 2016. That effort helped elect Senator Catherine Cortez-Masto in Nevada, after Harry Reid's retirement.

Renacci spokeswoman Leslie Shedd said she was unsurprised to see "outside groups running to the rescue of career politician Sherrod Brown."

"They know Sherrod Brown's ultra-liberal voting record is more in line with Elizabeth Warren and Chuck Schumer than it is with the people of Ohio, putting him in serious jeopardy of losing his Senate seat," said a statement from Shedd.

Most of the outside money that's been spent in Ohio this year has gone towards Tuesday's Columbus-area special election for the congressional seat vacated by Republican Pat Tiberi's departure to lead the Ohio Business Roundtable.

The special election contest between Franklin County's Democratic recorder, Danny O'Connor, and Republican state Sen. Troy Balderson of Zanesville is viewed as a barometer of whether Republicans will face an electoral backlash from voters who might be dismayed by President Donald Trump's actions.

Republican groups have spent more than $3.7 million so far on ads that try to link O'Connor, to House Democratic Leader Nancy Pelosi, and claim that he supports higher taxes and lower border security. Trump and Vice President Pence have visited to campaign for Balderson.