One of the biggest goals of the year for Democrats has been trying to find a candidate in Kentucky who is willing to run against Mitch McConnell, the Senate Republican leader. But the last man who tried to defeat him has new words of advice for his party: good luck.

Bruce Lunsford, a wealthy Louisville businessman who challenged McConnell in 2008, said Democrats face an uphill battle trying to win the seat. He said it would be a high-risk move for anyone with a political future, considering most of the rivals who have tried knocking off McConnell have never run for office again.

"There is really no sitting Democrat that I can think of right now that has the firepower, monetarily, or has enough gravitas to take him on significantly," Lunsford told ABC News. "I'd be surprised if anybody can run against him who thinks they have a further career in politics."

Democrats are eagerly awaiting an answer from Alison Lundergan Grimes, the Kentucky Secretary of State, who for months has been weighing whether to confront McConnell in the midterm elections next year. Democratic officials believe she is likely to make a decision in the next two weeks.

But the warning from Lunsford seems to be aimed directly at Grimes, 34, who he said has "a great future."

"I don't think there is any Democratic candidate who would be willing to risk the damage that he could do to them in a negative campaign," Lunsford said in an interview. "It's going to be very hard for Senator McConnell to lose."

Since his first race for the Senate in 1984, when McConnell defeated two-term Senator Walter "Dee" Huddleston, he has left a string of Democratic opponents in his wake:

In 1990, he defeated Harvey Sloane by 5 percentage points. Sloane had served two terms as the mayor of Louisville, but after his failed Senate race, he left Kentucky and never ran for office again.

In 1996, McConnell won by 8 percentage points. His opponent was Steve Beshear, who returned to practice law before running for governor in 2007. His Senate race against McConnell doesn't appear on his official state biography.

In 2002, McConnell defeated Lois Combs Weinberg by 30 percentage points.

In 2008, he received a scare from Lunsford. The contest was seen as highly competitive in the final days, but McConnell ultimately won by 6 percentage points.

"Mitch is probably the best pure politician the state has ever had," Lunsford said. "Not because he's a backslapper, but he's an intelligent politician. He's tough. He knows how to make it painful on an opponent."

The fight for control of the Senate is intensifying, with Democrats trying to defend their majority in 2014.

Republicans must pick up six seats to win control of the Senate, a goal McConnell is deeply focused on, along with his re-election to a sixth term. He is building a presidential-size campaign in Kentucky, with tens of millions of dollars in advertising.

Billy Piper, a former chief of staff to McConnell in the Senate, said McConnell has not made the mistake that has toppled so many of his colleagues: falling out of touch with his state.

"If you look at other races in the last couple of cycles where incumbents have been knocked off - in general elections or primaries-they became creatures of Washington and lost the connection to their state," Piper said in an interview. "McConnell goes home every weekend. It's the source of his strength."

Even without a declared opponent, the Senate race in Kentucky has already come alive with television advertising. Two Democratic groups started a strong offensive against McConnell on the airwaves last week, which is set to be countered this week by a Republican super PAC defending McConnell.

After actress Ashley Judd decided against challenging McConnell earlier this year, Democrats in Washington and Kentucky have been persuading Grimes to enter the race. She has drawn criticism from some fellow Democrats because she has not yet announced her intentions.

Her friends have pushed back against the criticism, saying she is traveling across Kentucky and talking to voters before she decides. They argue the election is still 17 months away and there is plenty of time.

"If she chooses to enter this race, she will not be afraid of Senator McConnell," said Jonathan Hurst, an adviser to Grimes. "And she will not be bullied by his tactics."