Carly Fiorina walks onto the stage to participate in the North Texas Presidential Forum at Prestonwood Baptist Church in Plano, Texas. (Photo by Stewart F. House/Getty Images)

Carly Fiorina hit 15 percent in national polls shortly after the second GOP debate. In New Hampshire she remains in double digits in many polls. Now in a series of national polls she appears in the mid-single digits. What happened? There are (at least) three explanations, which are not mutually exclusive.

First, maybe nothing happened. Her numbers got a bump because her debate performance was fresh in respondents’ minds. She simply fell back to her basic support, mid-single digits. This does not bode well for her future competitiveness.

Second, her support (or at least some of it) may be hampered by two candidates who seem even further “outside” than she, Donald Trump and Dr. Ben Carson. If her support rests with the grassroots and not with the mainstream voters (who could appreciate her foreign policy smarts and executive skill) then she is going to have a tough time beating out Trump, Carson, and Sen. Ted Cruz (R-Tex.).

Third, her support (or at least some of it) may have slipped over to Sen. Marco Rubio (R-Fla.), who is inching up ever-so-slightly ahead of Jeb Bush in many polls. These are the conservative and moderate Republicans who want a conservative agenda and viable competitor against the Democrats. These voters could have been intrigued by her but drifted off when they did not hear much from her after the debate.

Fiorina is in a tricky spot, running as a challenger but not one who is unhinged, knowledgeable or uncivil. There are a couple of ways she can go.

The most obvious is to go after Trump and/or Carson. Unlike Cruz, who fawns over Trump, she could continue the aggressive stance she took with him in the second debate. Attacking them as unserious, ill-equipped to take on Hillary Clinton (or Joe Biden) might pay off. The problem with this is the same that most combatants against Trump encountered: His voters are such low-information voters that they don’t care if he is irrational. They are mesmerized by his “angry man” routine. They might not show up to vote at all, but if they do, it will be as a protest voter  — a protest against not just political insiders but serious policy.

The better tactic however would be to start laying out an agenda. We’re past the point in the campaign where simply saying you are pro-life or anti-Washington is dysfunctional is sufficient. What does she want to do if she gets to be president, and how is she going to accomplish it? Why is she better than one of the other 14 candidates?

Now that Fiorina has raised some money, she will need to build a complete campaign. That means putting people on the ground in early states and bringing on people to help her enunciate  new, compelling things to say. She remains a highly skilled candidate, but if she wants to run in a jammed field she will need to step up her game. There are any number of issues she can pursue, including cyber-terrorism, international economics, worker training and education.

Whoever her target audience is — and it may be both grassroots and moderate sides of the party — she has to break through. Unless many candidates drop out soon and she can distinguish herself in the field it will be very difficult to do well in early primary states. Thinking good debate performances alone can sustain you is a mistake; a candidate needs to carry through in between the monthly events.