Republican presidential candidate Wisconsin Gov. Scott Walker speaks during a visit to the Iowa State Fair in Des Moines. (AP Photo/Charlie Neibergall)

Scott Walker can't seem to give a straight answer when it comes to the 14th Amendment and whether or not he believes in the idea of birthright citizenship.

In the last seven days he has been opposed to the idea, then revoked that support, then made clear to a donor that he wouldn't seek to end it, then said he has no position on it, then said he opposed repealing the 14th Amendment.  (WaPo's Jenna Johnson goes through all of the painful details of Walker's contortions on the issue.)

All candidates occasionally struggle to find the right (a.k.a. politically viable) answer on tough questions — especially candidates like Walker, who, while he has been in the national spotlight during his time as the governor of Wisconsin, has never faced the sort of scrutiny that comes with being a top-tier presidential candidate.  (Remember Jeb Bush on the war in Iraq.)

But, Walker's stumble on birthright citizenship is about more than just a relative greenness on the campaign trail. It speaks to the broader problem he now faces in the 2016 race: Is he an establishment conservative or a movement conservative?

Walker entered the presidential race convinced that he could straddle those two wings of the party. After all, he had been elected three times in four years in a blue-ish state, which appealed to members of the establishment who badly want to win in 2016, but he had also vanquished the powers of national organized labor in two of those elections, which made him a hero to movement conservatives.

Then Donald Trump happened. Trump's willingness to take a position on the extreme right of the party on immigration — round up people here illegally, send them home and build a massive wall — made the gap between the establishment (represented in the race by Jeb Bush and Marco Rubio) and the movement (Trump) too wide for anyone to straddle.

Walker tried, but failed. Trying to please both masters left Walker betwixt and between — satisfying neither. (This, by the way, is the same problem that has afflicted Rand Paul's campaign — caught between his libertarian base and the establishment of the party.)

After an unconvincing (and low energy) performance in the first debate earlier this month and significant slippage in polling in Iowa, it seemed clear that Walker needed to make a choice. And, last week, came a series of stories that suggested he was going to put himself on the Trump side of the party. (Yes, it is somewhat unbelievable that there is a "Trump" side of the GOP. But there is.) "Fading in the polls, Scott Walker aims to attract Trump voters," read WaPo's headline on a story that reported this:

In a conference call, one-on-one conversations and at a Tuesday lunch, the Wisconsin governor and favorite of anti-union conservatives told backers that his campaign is shifting to a more aggressive posture and will seek to tap into the anti-establishment fervor fueling the rise of Donald Trump and other outsider candidates.

That story was followed by a week of mishigas on the 14th Amendment.  Not so good.

Walker's camp, of course, is casting his variety of positions as totally consistent. "He has been saying this all week long," Walker spokeswoman AshLee Strong told Jenna. "You have heard him say that countless times. I know what you're asking for but just because you're not satisfied with his answer doesn't make his any less worthy."

Ha! Good one! (Sidebar: I think politicians would win a lot more good will if they occasionally were willing to say: "Look, I didn't have all of my thoughts together when I first responded on [fill in the blank] issue. As a result, I didn't express myself right. Here's what I really think.")

Walker is a man caught in the middle of the GOP right now — and not in a good way. He needs to pick a side and fight like hell to win the primary within a primary to be the preferred candidate for that side of the party.  Another week like the last one will further add to lingering doubts within GOP circles about whether he's ready for a stage this big.