Next week Hillary Clinton will release "Hard Choices," a memoir of her years as secretary of state. The book is Clinton's first since Living History, a memoir of her childhood, Ivy League education, marriage to Bill Clinton and time as first lady.

So: Clinton's first book covered the period from her birth in 1947 through 2001. Her second book covers 2009 through 2013. What about the eight years in between, from 2001 to 2009? That was the time Clinton served as a U.S. senator, and it is the only part of her life she has not seen fit to write a book about.

There's a reason for that. Clinton's Senate career is the awkward middle-distance period in her case for the presidency. When she speaks in public these days -- she'll be doing more after the book is released -- Clinton tends to talk about either her time at the State Department or her years in the White House. The Senate? Not so much.

Clinton was a lackluster, team-player senator. There was just one big moment in her career as a lawmaker -- her vote to authorize U.S. forces to go to war in Iraq -- and it's one many of her supporters would like to forget.

Clinton's Senate career started with accusations that she was a carpetbagger, which of course she was. As her husband's second term came to an end, she had a spike of popularity as the wronged wife, and rumors spread that she was considering a political run.

Born and raised in Illinois — never a resident of New York — Clinton chose to run in the Empire State because it was politically blue and, most importantly, happened to have an open Senate seat in 2000. To show New Yorkers she was one of them, Clinton and her husband split their 1999 summer vacation between their usual choice, Martha's Vineyard, and New York's Finger Lakes region.

When Clinton indicated she would run, other New York Democrats obediently got out of the way. Nomination in hand, she ended up with a weak Republican opponent and a solid victory.

Clinton approached her time in the Senate differently from other ambitious politicians. A Ted Cruz or a Marco Rubio comes to the Senate to make a name for himself, to step up to the national stage. Clinton had all the celebrity and name recognition in the world. She needed something to show that she was a statesman in her own right, and not just the president's wife.

Once in the Senate, Clinton surprised many with her low-key approach. "In public gatherings on Capitol Hill, she is now often the last to speak, waiting her turn in deference to ranking members of the Senate," the New York Times reported in April 2001. The paper noted that Clinton joined a prayer group led by Republican colleagues and assured Democrats she intended to be "a workhorse, not a show horse."

And mostly, she was. Clinton worked on recovery funding for New York after the September 11 attacks. She voted against the Bush tax cuts. She worked on veterans issues. On broadband access. On electronic medical records. She voted against the nominations of Supreme Court Justices John Roberts and Samuel Alito.

It was a completely unremarkable record, not notably different from most of her 99 Senate colleagues. And then came the October 2002 vote to authorize war in Iraq. Sen. Clinton had proven herself a team player, but this time her team was divided. What to do?

Clinton agonized, finally coming to the conclusion that Saddam Hussein was working to build weapons of mass destruction. "This is probably the hardest decision I've ever had to make," she said on the Senate floor. "But I cast it with conviction."

Clinton's pro-authorization vote would haunt her when she ran for president in 2008. Her opponent, Barack Obama, had conveniently not arrived in the Senate until more than two years after the vote, freeing his supporters to slam Clinton's decision daily. Even now, it is not unusual to hear Democrats complain about it.

If Clinton were to face a competitive primary in 2016, it might still be a problem. But that doesn't seem likely. And by 2016, the Iraq vote will be 14 years in the past. Its impact will have faded.

Along with the rest of Clinton's Senate career. In 2008, Clinton thought her record as a lawmaker (plus her experience as first lady) qualified her to be president. But there just wasn't much there. No surprise that now, she doesn't talk a lot about her years as Sen. Clinton.