Back in 2000, when Hillary Clinton was still First Lady and running for the US Senate, I thought she would be a bad fit for the job. Clinton was clearly very smart and talented, but I believed that her particular gifts made her a natural Cabinet Secretary: the very job that she couldn't hold as the sitting President's spouse.

I thought Hillary would be better running a department, which would allow her to draw upon her deep mastery of policy detail, than she would be as a legislator and campaigner. She wasn't the natural stump politician that Bill was, and I didn't think she would do well in the deal-making, back-slapping world of the Senate. I was wrong.

Clinton was an extremely effective Senator, and got re-elected without breaking a sweat. She not only adapted to the Senate, but she mastered it, becoming a powerful and influential member. So I was wrong, because I had underestimated Hillary Clinton.

Then, when she had lost her closely-fought nomination contest with Barack Obama and President-Elect Obama asked her to be Secretary of State, I thought that it was a mistake. Yes, of course, I thought she would make a great Cabinet Secretary, that it was a natural position for her gifts. But now that she was being offered state, I thought that she would be great leading any department but State.

I thought Clinton would be undermined by being the emissary for another powerful male politician, especially by one who had beaten her. She had been Bill's surrogate, and now she would be Barack's. The Secretary of State needs to a solid relationship with the President, or (more accurately) needs other foreign leaders to see her relationship with the President as solid. I disliked seeing Clinton in a job which made her so visibly dependent upon a male patron.

I was wrong. Again. Because I had underestimated Hillary. Again.

Clinton was a powerful and effective Secretary of State, who obviously had Barack Obama's ear and who was clearly respected by foreign governments as a heavyweight in her own right. Being Obama's deputy did not diminish Clinton; it elevated Obama. Clinton's gravitas underscored Obama's seriousness, and sending Clinton always signaled that Obama was taking someone seriously.

I was proud of Clinton's service. My favorite moment was during a meeting with various Arab leaders shortly before the Arab Spring, in which Clinton tried to persuade them to loosen up and reform their systems before they had problems. (Yes, she told them this before the Arab Spring. When you're right, you're right.) They threw back their reflexive deflection, "Why don't you get Israel to reform its behavior?" to which Clinton answered, without missing a beat, "We can't get a lot of our allies to do what we'd like them to do." Boom! There it is.

So I've been wrong about Hillary Clinton, on a consistent and semi-regular basis, for a decade and a half. I've given her my mealy-mouthed doubts, always saying that of course she's very qualified, but not for whatever particular job she was up for. I didn't think of it as a sexist objection, but let's be frank: I discounted her qualifications in every actual case, so that I would speak of her as gifted in the abstract but unqualified whenever she was up for an actual job.

Well, I'm done making that mistake. I've been wrong about Hillary Clinton a number of times. But I'm not going to underestimate her again. She has always surprised me, always exceeded my expectations, and I am never going to discount her again.

I'm ready for Hillary. But even if I weren't, Hillary is ready.