Hagan is also the strongest fundraiser of the four, ending the last reporting period with more than $1.3 million in the bank.
Democrats won big in New Hampshire in November, which bodes well for Shaheen, though she has the least amount of money in her campaign coffers, ending the October quarterly with only $338,000.
Although Republicans loudly have criticized Udall, none have stepped forward yet to challenge him. He has about $1.1 million in his war chest.
Merkley ended the last reporting period with nearly a half-million dollars in the bank, and is expected to be safe in 2014.