Sen. Mark UdallMark Emery UdallDemocratic primary could upend bid for Colorado seat Picking 2018 candidates pits McConnell vs. GOP groups Gorsuch's critics, running out of arguments, falsely scream 'sexist' MORE (D-Colo.) raised $2 million in his first fundraising quarter since Rep. Cory GardnerCory Scott GardnerDurbin: Senators to release immigration bill Wednesday GOP senators eager for Romney to join them Gardner: Bipartisan DACA solution possible despite Trump's 's---hole countries' comment MORE (R-Colo.) jumped in the race against him.

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The strong fundraising quarter boosts Udall's cash on hand to $6 million.

Gardner has yet to announce his fundraising totals. He had $800,000 in the bank as of the end of 2013 — but that was before his switch to the Senate race and GOP party leaders' rallying around him.

Polls have found a tight race between the two.