There is only one Republican endorsement that matters in New Hampshire's first-in-the-nation primary: US Senator Kelly Ayotte.
Ayotte, tied in polls of her own reelection battle next year, has not signaled whether she will endorse any candidate. But if she wants to endorse, this might be the week to do it.
A WBUR poll of New Hampshire Republicans out this morning shows considerable volatility among the so-called "establishment" class of candidates (and Ayotte's most likely endorsement recipients). While Donald Trump continues to hang onto the first-place spot, everyone else continues to shift positions. In the last two months, the second-place spot has belonged to Ben Carson, former Hewlett Packard CEO Carly Fiorina, Ohio Governor John Kasich and US Senator Marco Rubio of Florida.
But the battle for second place isn't even the GOP's most interesting contest. Republicans want to know who will emerge among Rubio, Kasich, former Florida governor Jeb Bush, and New Jersey Governor Chris Christie as the moderate/establishment choice (Some Republicans also include Fiorina in this camp).
That question is anyone's guess. Ayotte is the only one who can provide the answer.
But to be sure, her decision is complicated.
Rubio ran television ads in her defense when she voted against the Manchin-Toomey amendment on background checks for guns. As chairman of the Republican Governors Association, Christie spent millions of dollars attacking Ayotte's foe, Governor Maggie Hassan, in her reelection bid last year (even then, Republicans expected Hassan would challenge Ayotte in 2016).
However, endorsing Bush would give Ayotte access to his national fundraising base -- something she will need for her own race. Kasich also seems like a safe bet: His Ohio background could mean he is the most electable in a general election. What's more, Fiorina on top of the ballot could blunt any energy female voters have to elect Democrat Hillary Clinton as the first female president, which could have implications for Ayotte's own race.
Last but not least, Ayotte has a personal friendship with US Senator Lindsey Graham, with whom she watches movies with her children.
The easiest thing for Ayotte is to not endorse. It is something of a New Hampshire tradition to cheer from the sidelines when facing a major election in the upcoming year to avoid upsetting members in their own party. Of the dozen candidates running or exploring runs for major office in New Hampshire next year, only Hassan, US Representative Annie Kuster, and Kuster's potential challenger, New Hampshire House Majority Leader Jack Flanagan, have endorsed a presidential candidate.
Four years ago, on Nov. 20, Ayotte endorsed Mitt Romney in the state's presidential primary. That might have been an easier decision given lack of moderate candidates in the field that year. However, the timing of her endorsement was perfect: Romney was trailing in national polls for several months to several different people. Her endorsement coincided with the Romney comeback. In other words, her timing and her endorsement mattered.
This time, her endorsement could matter even more. And if she chooses to do it soon, it could fundamentally shape the race, giving a needed boost to Bush or Christie or anyone else. If she did it now, with 97 days until the primary, she would get full credit as the kingmaker with enough time for her backing to matter.