the strength of Sanders’s challenge — particularly in the states hosting the first two nominating contests — is starting to get attention.

“Primary voters in New Hampshire are looking around,” said Democratic strategist Brad Bannon. “They at least want to shop around a little bit before buying. Based on that alone, it’s probably time for the Clinton campaign to take Sanders seriously.”

One of the problems that the Sanders surge poses for Clinton is that Democrats say there’s a risk in taking him head on.

Doing so could rally his supporters, alienate liberals the Democratic nominee will need in the fall of 2016 and elevate Sanders as a challenger.

“They’re not going to go after him publicly, and it’d be wrong to do so,” said Democratic strategist Hank Sheinkopf, who worked on then-President Clinton’s 1996 reelection bid. “She needs to keep slogging along and make the kinds of policy arguments that will eventually make some of the uniqueness around Sanders dissipate.”