2. Why is she declaring now? You can sort the reasons into three categories. The first is legal. Politico broke the news last Friday that Clinton had signed the lease on a huge office space in downtown Brooklyn to house her campaign. That signature started the clock for Clinton to comply with Federal Election Committee rules that mandate that someone must file paperwork declaring their candidacy within 15 days of conducting campaign activities. The second is political. When Clinton came under fire for her handling of emails as secretary of state, her response was widely panned—she hesitated to reply, then held a perhaps ill-advised press conference in an imperfect venue with disappointing answers. Democrats panicked and worried that Clinton's problem was that without a campaign apparatus she wasn't ready to reply quickly to attacks—a problem made more urgent by the entrance of Republicans into the race. The third is human. "We just wanted to get this thing over with and get on with it," an adviser told Glenn Thrush. And who can blame them? Her declaration is a surprise to no one except Mike McCurry.

3. What will her campaign be about? This is perhaps the biggest unanswered question. Everyone knew she was running; but why? What will her campaign theme be? Is it about income inequality? Foreign policy? Change? Staying the course? We still don't know. How Clinton will handle the Woman Question is also a subject of much speculation. During the 2008 campaign, she generally avoided relying on gender, but her concession speech ("18 million cracks" in the glass ceiling) was hailed as a feminist classic, and the way she's deployed her new grandmotherhood on the trail has given some people the impression that she'll focus on her candidacy as historic and pathbreaking for women. Trying to figure out just how much she'll embrace the populism of the Democratic Party's left is also up in the air.

4. What has she learned since 2008? And does she really want to be president? Forget "Two Americas"; conventional wisdom has settled on a "two Hillarys" theory of the 2008 campaign. Early on, there was Inevitable Hillary, a distant, aloof campaigner who took her nomination for granted and botched it. Later, there was Fighter Hillary, a surprisingly adept retail politician who showed genuine emotion and threw back boilermakers with union men. Besides, her campaign was riven by incredible backbiting, clashing egos, and bad behavior, as Joshua Green reported in The Atlantic.

Some of her early moves this time around have fed an impression that she's back in the first mode. (For a long and excellent dive into Clinton's skills as a campaigner and how much they matter, read Jason Zengerle's New York feature.) And does she really want this? That question is perhaps inextricable from what her campaign will be about, but Clinton has been headed toward a White House run for so long that one wonders whether she's just doing it automatically. Those close to her who doubted a run questioned whether she still had the fire in her belly, but the declaration alone isn't enough to answer the question.