For Grimes and other coal country Democrats, embracing that label is more than a political convenience. It's vital for political survival.
In one of the year's top Senate races, McConnell and his Republican allies have poured millions into Kentucky to link Grimes to President Barack Obama and what they call his "war on coal," betting that voters who blame Obama for a devastating wave of mine closures and job losses will not put a fellow Democrat in the Senate.
Whether Grimes can convince them she is a different breed of Democrat, one who can stand up to Obama and the party's green lobby and fight environmental regulations, will play a big role in her November battle with McConnell and help determine which party controls the U.S. Senate.
The fight in Kentucky echoes an argument playing out in Senate races in other conservative states such as Louisiana and Alaska, where Republicans claim their Democratic opponents will be a rubber-stamp for an Obama agenda that imposes big-government solutions on every problem.
That argument will be in the spotlight next week, when the administration unveils new regulations limiting carbon emissions for existing power plants that already have the coal industry and its political allies gearing up for battle.
"I don't agree with the president's war on coal, I think it's wrong for Kentucky," Grimes said after a primary victory last week that set up her election fight against McConnell, the Senate Republican leader.
"I will fight to make sure that coal has a long-term place in our national energy policy," she said. "I won't answer to the president."
Obama, who lost Kentucky by 22 percentage points in the 2012 election, has not visited Kentucky to support Grimes, and national Democratic groups so far have spent modestly on ads targeting McConnell.
Polls show Grimes and McConnell enter the general election campaign in a dead heat, giving Democrats hope of stealing a seat from Republicans in a year when they are desperately trying to hang on to their six-seat Senate majority.
During her campaign, Grimes, currently Kentucky secretary of state, has promised to create jobs, fight for equal pay for women and for a higher minimum wage.
But the debate over coal has become one of the most prominent issues in Kentucky, which generates more than 90 percent of its power from coal and ranks third among states in U.S. coal production behind Wyoming and West Virginia.
The industry has been in decline for decades as technological improvements and low prices for coal's natural competitor, natural gas, have undermined jobs.
The state still prides itself on its coal history and voters in Appalachia blame the Obama administration's regulatory rules and its alliance with environmental groups dedicated to phasing out fossil fuels for coal's woes.
'Very leery'
That puts more pressure on coal-friendly Democrats like Grimes -- along with Senate candidate Natalie Tennant and U.S. Representative Nick Rahall, both of West Virginia, who also have criticized Obama's coal agenda -- to prove the sincerity of their break with the national party.
"It makes someone like me very, very leery of Grimes," said Tim Birman of Harlan, a 38-year-old single father who lost his coal mining job years ago and now drives to construction jobs in a nearby county.
"Obama and the Democrats have done so much to hurt the coal industry, it makes me question how trustworthy she can be."
On a recent bus tour through eastern Kentucky's battered coal country, Grimes repeatedly promised to fight the new environmental regulations and help attract new businesses to the counties hit hardest by coal's plight. She questioned how much McConnell had done to help.
"We have lost thousands of good coal jobs on his watch, not mine. We have seen overburdensome regulations come into effect on his watch, not mine," she told about 50 voters at a Harlan community center. The scariest thing to McConnell, she said, was a "pro-coal Democrat."
Grimes said she would push for tax incentives to develop clean coal technology and work with other pro-coal Senate Democrats like West Virginia's Joe Manchin to develop a comprehensive energy policy with room for coal.
McConnell, she said, has been more interested in partisan politics during his 30 years in the Senate than in working on behalf of coal interests.
"The people of Kentucky know who I am. They have spent millions on these false, negative ads about me and it has not made a difference," Grimes said on her bus after a day of rolling up and down mountainous roads for a series of coal-country rallies.
In response, McConnell rarely passes up the chance to utter the phrase "war on coal" and link Grimes to Obama and Senate Democratic leader Harry Reid, whose 2008 comment that "coal makes us sick" has made him deeply unpopular in Kentucky.
"My opponent is in this race because Barack Obama and Harry Reid want her in this race," McConnell said after beating a Tea Party-backed businessman in the Republican primary.
The coal industry is still celebrated proudly in Kentucky. The most popular bumper sticker on trucks in Harlan County is still "If You Don't Like Coal, Don't Use Electricity," but the skeletons of abandoned mine operations and the high unemployment rates -- nearly 17 percent in Harlan in March -- are a testament to the industry's decline.
Coal mines and preparation plants in eastern Kentucky laid off another 2,232 employees in 2013, leaving employment in the region's coalfields at 7,332 - barely half of what it was in the summer of 2011, a recent state government report said.
'Never be like it was'
"I have come to accept the fact that the coal industry will never be like it was," said George Noe, 43, who works the night shift at one of a handful of operating mines in Harlan County, which decades ago had more than 180 thriving coal operations.
"I would just like to hear somebody say they are going to work with us to keep what's left of the industry, and find a way to keep at least a few jobs down here," said Noe, who is undecided in the Senate race.
Some leaders of the state's coal industry are wary of Grimes, who does not have as much history with them as McConnell.
"She hasn't been very specific about how she can help us on coal," said Bill Bissett, president of the Kentucky Coal Association, which does not make political endorsements.
Two independent groups backing McConnell, the U.S. Chamber of Commerce business group and a Super PAC run by a former adviser to President George W. Bush, already have spent more than $2.8 million primarily on ads hitting Grimes on coal, and the race is expected to be among the country's most costly.
Stephen Voss, a political scientist at the University of Kentucky, said Grimes could find her candidacy "a hard sell" with voters as long as the Senate race was dominated by the "war on coal" debate.
"No matter what she believes and how she is going to vote, she is still going to put that party that backs those anti-coal policies in charge of the Senate," Voss said.
