Rep. Carolyn McCarthy will not challenge Sen. Kirsten Gillibrand in a Democratic primary.
McCarthy, a thorn in Gillibrand’s side of late, had said she would take on the newly appointed senator in 2010 if no one else did.

But McCarthy has reversed course, citing personal issues.

“I’m not running,” she said Thursday afternoon.

That further clears the field for Gillibrand, who has had difficulty coalescing her delegation around her bid. Some other New York lawmakers were rubbed the wrong way by her rapid ascent to the Senate, ordained by Gov. David A. Paterson when Sen. Hillary Rodham Clinton became secretary of State earlier this year.