He may not be The Boss, but The Kid lent his high-octane rock & roll to the final rally of Mitt Romney's 18-month campaign, on the eve of the US presidential election. Kid Rock late Monday was the star attraction at an arena in New Hampshire, the state where the Republican nominee's presidential bid began 18 months ago, and several thousand supporters gave him and the Romneys a rousing welcome. Romney and President Barack Obama are locked in a neck and neck election that will come down to a handful of swing states, and as the candidates brought their months of raucous campaign rallies to a conclusion, they roped in major musical acts to drive home their message. For the president, it was legendary rocker Bruce Springsteen -- nicknamed "The Boss" -- and hip-hop king Jay-Z, who raised eyebrows by changing the lyrics of one of his songs to: "I got 99 problems but Mitt ain't one." Springsteen offered some political nuggets on stage in Wisconsin and later in Ohio, including describing how he has been writing music for 30 years "about the distance between the American dream and American reality." "Our vote tomorrow is the one undeniable way we get to determine the distance in that equation," said Springsteen, who played a short set in Madison, Wisconsin with songs like "No Surrender" and "Promised Land." Unlike Springsteen, Grammy nominee Kid Rock opted not to "talk politics," saying he preferred to "leave that to the professionals." The music -- including "Born Free," the rousing anthem that became a staple on the Romney campaign -- transitioned to politics, with Kid Rock introducing Romney and his wife Ann, who took the stage to a deafening roar.