Congressional races saw record-shattering fundraising numbers this year, with Democrats pouring money into candidates challenging Republican incumbents.Why it matters: Democrats heavily invested in these contenders with the hope of flipping the Senate. The races brought in an outpouring of small-dollar donations.The big picture: Though Democratic campaigns collected many millions of dollars this election cycle, several races in key states have resulted in losses.South CarolinaJaime Harrison, who raised $108.9 million, lost to Sen. Lindsey Graham.Kentucky: Amy McGrath, who raised $90 million, lost to Sen. Mitch McConnell.Maine:Sara Gideon, who raised $69.5 million, lost to Sen. Susan Collins.Texas:Mary Hegar, who raised $24 million, lost to Sen. John Cornyn.What they're saying: "You wasted a lot of money," Graham said in his victory speech Tuesday night after defeating Harrison. “This is the worst return on investment in the history of American politics."The bottom line: Despite picking up Senate seats in Colorado and Arizona, Democrats' hopes of winning control of the Senate faded as they lost a series of high-profile races.