Former President Barack Obama, in an address to liberal donors, warned candidates not to go too far left and sought to calm those who were concerned about the state of the Democratic primary.

By LIsa Lerer @ NYTimes.com, Nov. 15, Updated 10:56 p.m. ET

WASHINGTON — Former President Barack Obama offered an unusual warning to the Democratic primary field on Friday evening, cautioning the candidates not to move too far to the left in their policy proposals, even as he sought to reassure a party establishment worried about the electoral strength of their historically large primary field.

Speaking before a room of wealthy liberal donors, Mr. Obama urged Democrats to remember the long, combative slog of his primary campaign against Hillary Clinton in 2008, arguing that the 16 month battle ultimately made him a stronger general election candidate.

“For those who get stressed about robust primaries, I just have to remind you I had a very robust primary,” [....]