Freshman Rep. Tom CottonTom CottonCotton: I hope we go back to health care next year Sunday shows preview: GOP gears up for Senate tax reform push A simple way to make America even greater is fixing our patent system MORE (R-Ark.) officially launched his campaign against Sen. Mark PryorMark PryorMedicaid rollback looms for GOP senators in 2020 Cotton pitches anti-Democrat message to SC delegation Ex-Sen. Kay Hagan joins lobby firm MORE (D-Ark.) Tuesday evening in his hometown of Dardanelle, Ark., setting up one of the most closely watched Senate match-ups of the 2014 election cycle.

Cotton laid out an anti-Washington, anti-Obama message consistent with his hard-charging conservative views, blasting "crony capitalists" throughout the speech and tying Pryor to President Obama and his signature healthcare law, both of which are deeply unpopular in the state.

"It's time to say 'enough.' Arkansans need a senator who will stand with them and stand up to Barack ObamaBarack Hussein ObamaReport: FCC chair to push for complete repeal of net neutrality Right way and wrong way Keystone XL pipeline clears major hurdle despite recent leak MORE, a senator who will say 'no more' to the crony capitalism, the giveaways, the reckless spending, the unfair taxes, the job-killing regulations, and the concentration of unaccountable, unconstitutional power in Washington," he said. "Arkansans need a senator who won’t just stand by and accept the status quo.  I will be that senator."

Cotton's announcement has been long expected. He's been mulling a run for months, and sources close to Cotton told The Hill last week that he'd made up his mind.

The former Army Ranger ripped Pryor, accusing him of abandoning Arkansas for his party.

"Mark's been running for office for almost 25 years. Every time, he says 'Arkansas comes first.' It’s not so. Over the last four-and-a-half years, for Mark Pryor, Barack Obama comes first," he said. 

"Mark Pryor is the reason ObamaCare is the law today. He could’ve stopped it, but he stood with Obama instead. Mark Pryor voted for Obama's wasteful stimulus that added almost a trillion dollars to the debt, without lasting job growth. Mark Pryor voted for Obama’s amnesty plan for illegal immigrants that will hurt Arkansas families by driving up unemployment and driving down wages, without securing the border. ... Mark Pryor doesn’t put Arkansas first any more — Mark Pryor puts Barack Obama first."

The campaign is expected to be a hard-fought one, and most observers view it as a must-win for the GOP if the party hopes to win back Senate control. A number of recent polls in recent days show a close race.