As news spread Monday that former top-tier candidate Scott Walker was suspending his presidential campaign, colleagues and friends kept asking me: Are you surprised? What happened?

I started covering Walker in late April when he was an early favorite in Iowa, poll numbers were high and donations were rolling in. Since then, I have interviewed countless Walker supporters as I traveled thousands of miles with him — following the "Walker Winnebago" down gravel roads in rural Iowa and watching his rented Harley-Davidson Road King hug bends in New Hampshire's mountains. I discovered Wisconsin cheese curds (best when fried and dipped in ranch dressing) and got to know a mild-mannered Midwestern presidential candidate who seemed enamored with retail politics, campaign strategy, social media and whatever his two college-aged sons deemed interesting. I watched as Walker's campaign quickly devolved, poll numbers fell, staff members grew frustrated and donors lost hope.

My colleagues and I are still unraveling exactly what went wrong, but here are nine things I learned about Walker on the trail that help explain how he ran his campaign — and why he decided to end it:

1) It was unclear exactly why Walker wanted to be president.
Walker has only been the governor of Wisconsin for 4½ years, following more than eight years as the Milwaukee County executive. Yet unlike many young governors, he had a strong national profile — along with the admiration of many wealthy Republican donors — because of the dramatic, highly publicized battle he waged against his state's public-sector unions in 2011, soon after becoming governor. In severely weakening those unions and then winning a recall election, Walker earned the support of fiscal conservatives and the tea party, and angered liberals around the country.

So with a seemingly wide-open presidential primary, it made sense for Walker to run, pitching himself as a Republican loathed by Democrats who has had success in beating them. But Walker often seemed to struggle to explain exactly why he would be a better president than the other Republicans running. He seemed to write much of his domestic and foreign policy as he went along, rather than coming to the race with a clear vision of where he would take the country. For many voters who are often tired of uncompromising career politicians and gridlock in Washington, perhaps Walker's promise to fight Democrats just wasn't enough.

2) Walker seemed to lack an inner circle.
For a candidate who has been campaigning since he was 22, Walker seems to lack a defined coterie of trusted political confidants — or even longtime best friends from outside the political world whose advice he trusts. Walker has long been rather independent, serving as his own political strategist and trusting his own instincts above all else, sometimes frustrating his staff by making decisions without their counsel.

As Walker launched his presidential bid, advisers who had been key to his breakout success in Wisconsin were suddenly sidelined or isolated at a super PAC, which is legally barred from coordinating with the campaign. Walker hired a team of campaign staffers from outside the state who moved to Madison and rushed to get to know him. Walker has long said that his wife, Tonette Walker, is his closest confidant, along with their two college-aged sons, Matt and Alex. Walker nearly always says "we" instead of "I" when discussing how he decided to run for president. In the end, Walker said his decision to suspend the campaign was one he discussed with his wife and God.

3) For an everyman candidate, his campaign events were often elaborately staged.
In late July, Walker held a town hall at a family-style restaurant in Red Oak, a town with fewer than 6,000 residents in western Iowa. An advance team with a moving van of equipment arrived hours early to hang up flags, set up a sound system and arrange a stage with tiered seating to provide a backdrop of Iowans. Walker arrived with a large entourage: his security detail, campaign manager, personal aide, full-time campaign photographer, two Iowa-based staffers and a horde of low-level employees who handed out brochures. As he spoke for roughly an hour, one man on the stage had to shield his eyes from a bright spotlight.

That's the level of staging that Walker enjoyed during nearly every campaign stop during his first month on the trail — which worried some supporters, who considered the elaborate set-ups a waste of money so early in the campaign. These glitzy events seemed more suited to a candidate who had already locked down the nomination, but they matched Walker's forceful confidence — he truly considered himself a front-runner who could win over most voters in most states.

4) Money has long been a problem for the Walker family.
Unlike many candidates for president, Walker lacks personal wealth. As a young state lawmaker, he made less than $40,000 per year. When he became the Milwaukee County executive in 2002, he kept a campaign promise to return much of his salary, a total that he says reached $375,000 by 2010. As governor, Walker was paid nearly $148,000 per year, in addition to free housing in the governor's mansion, taxpayer-provided vehicles and other perks. He also received a $45,000 advance for the 2013 book he wrote about his fight with the unions.

But financial disclosures revealed that Walker has tens of thousands of dollars in credit card debt, including a large balance on a card with an interest rate of more than 27 percent. His two sons have taken on at least $100,000 in student loan debt and have yet to graduate from college. It's clear that unlike some candidates in the race, Walker could not afford to absorb any potential debt of a presidential campaign. Several donors said Monday night that fear of debt was a driving factor in Walker's decision to so suddenly step out of the race.

5) Walker knows how to stay on message — but seems lost when questions keep coming.
Early in the campaign, Walker and his backers would brag about his ability to relentlessly stay on message: He again and again repeated the same campaign speech. He gave reporters the same answers to questions about issues of the day. He memorized his announcement speech and recited it. This often left him sounding robotic and not fully answering the questions he was asked.

But when reporters and cable news show hosts pushed for specifics, Walker would often slip up, making comments that didn't quite make sense or taking stances he didn't mean to take — but then hesitating to take a different position or admit that he had misspoken, perhaps for fear of cementing an image of being a flip-flopper. Instead, he appeared to lack clear stances on a number of issues, including birthright citizenship and the U.S. response to the Syrian refugee crisis. Several supporters exploded with frustration when Walker called building a wall along the Canadian border a "legitimate" idea — and then waited more than a day to make clear that he did not actually want to construct a wall along the 5,252-mile northern border.

6) Walker seems uncomfortable with direct confrontation.
Ahead of the first Republican debate, I watched hours of video footage from Walker's previous debates in Wisconsin. In a few of these, Walker had the opportunity to ask his opponent a question and passed. Instead, he stuck to his talking points and avoided confrontation.

This is a candidate who built his presidential campaign on the premise that he was a fighter — yet he seemed uncomfortable confronting people face to face, especially fellow Republicans. On the early campaign trail, Walker ignored protesters, maneuvered out of conversations that turned testy, rarely held town halls and avoided follow-up questions from reporters whenever possible.

In recent weeks, Walker tried to shift course. He became more aggressive by yelling back at a protester at the Iowa State Fair, criticizing fellow Republicans, challenging Trump at the latest debate, scheduling more town halls and swearing that he would "wreak havoc on Washington." But all those actions sometimes felt forced and out of character.

7) Walker is no world traveler.
In June, I followed Walker to Quebec City, where he attended a conference for Canadian and U.S. officials from the Great Lakes region. When he addressed the audience, Walker marveled at the pitchers of water sitting on the conference tables in the palatial hotel and said he drank from them without hesitation: "There are plenty of places around the world I go to that I would not dare do that. I would not be drinking water unless they brought it to me in a bottle, and I could make sure the top had not been turned … because I wouldn't know if I would get sick or not."

The list of countries Walker has visited is not lengthy or exotic — and most trips came this year as he rushed to learn more about foreign policy so he could speak with the same ease as many of his well-traveled rivals. While Walker's knowledge deepened this year, he still struggled to project that authority. On a majority of foreign policy questions, he would pivot to two major talking points: the need to destroy "radical Islamic terrorism" and to embrace Israel as an ally.

8) Walker gets tired.
Days after launching his campaign, Walker pulled an all-nighter when his flight was diverted because of weather. During campaign stops in South Carolina the next day, Walker was visibly exhausted, his eyes red and puffy. He started slurring words, turning "Harley" into "Farley" and "ISIS" into "aces." Although the crowd laughed and clapped as he recounted his harrowing travel adventures, they didn't get to see his best self. The same was true as Walker rode a rented Road King through New Hampshire over Labor Day weekend, becoming frustrated and mixing up his words as he addressed a swarm of reporters at the end of the first day of the ride. If Walker stayed in the race, the grueling schedule likely would have continued.

9) He is a pragmatic strategist who knows how to spot opportunities.
When Walker was in the state assembly, the Democrat serving as the Milwaukee County executive resigned amid scandal over changes to the pension system. Walker jumped into that race and won. In 2006, he tried running for governor but dropped out when it became clear that he didn't have the fundraising power of other candidates. He came back in 2010 and won.

Walker has had a knack for studying the political currents, jumping at opportunities; knowing when to join a fight — and knowing when to leave one.