As Republicans battle for the GOP presidential nomination, dominating news coverage with their first nationally televised debate this week, the story of Hillary Clinton's Democratic campaign is getting more interesting. One big reason is that her predicted coronation seems somewhat less assured than it did a few weeks ago.

Supporters of Vice President Joe Biden are stirring the pot, telling reporters that he still may jump into the Democratic race and give Clinton a run for her money. And pollsters of both major parties say many voters don't consider Clinton to be trustworthy, a growing vulnerability. These voters see her as too willing to cut corners and ignore the rules that apply to others in order to advance her political interests. Among the examples cited by critics: her use of a private email system while she was secretary of state, which her detractors say was designed to avoid media and congressional scrutiny; her closeness to big-money interests; her lack of detail on some issues such as an emerging free trade agreement being negotiated by President Barack Obama's administration, and her disdainful treatment of the news media as she runs a tightly controlled and highly insular campaign.

For her part, step by step, policy by policy, speech by speech, Clinton is trying to reconstruct President Barack Obama's winning coalition from 2008 and 2012 as the best way to succeed him in the White House. This means courting female voters, especially single women, Latinos, African-Americans, young people, new voters and liberals. David Axelrod, who formerly served as Obama's chief strategist, recently told the New York Times, "There's no doubt she understands coalition politics and she is burnishing her coalition."

Clinton, for example, has been regularly addressing issues important to African-Americans, expressing support for policies that would lead to less incarceration of black men, more stringent control of guns and, she argues, fewer police abuses. She is also hammering the GOP for being out of touch with everyday Americans, a charge aimed at courting the middle class with rhetoric regularly used by Obama.

"A lot of Republicans may talk about having new ideas and fresh faces, but across the board they're the party of the past, not the future," Clinton told Virginia Democrats in late June. "And when you ask them, what are your new ideas on the economy, well, you guessed it – more tax cuts for the very wealthy and fewer rules for Wall Street. Now, if that sounds familiar, it's because those are exactly the same top-down economic policies that failed us before. Americans have come too far to see our progress ripped away."

Clinton is still far ahead of all her announced Democratic opponents, according to the polls. But her unfavorable ratings have been increasing.

And there is the potential challenge from Vice President Biden, which could be cause for concern in Hillaryland. Biden says he still hasn't decided whether he will run against her for the 2016 Democratic presidential nomination, but he really isn't Clinton's main problem. She can be her own worst enemy.

Pollsters and political strategists of both major parties say it's very possible that Clinton could make a major misjudgment, as she did in 2008 when she underestimated Obama's appeal as a fresh face and a new voice of progressive change. She was the early leader in the polls that year only to falter and lose the Democratic nomination to Obama.

Sen. Bernie Sanders, an independent and self-described socialist from Vermont, is the closest thing to a real threat against Clinton so far as he also seeks the 2016 Democratic presidential nomination. Sanders has been drawing big crowds that cheer his unabashedly liberal message. And one never knows which other Democrats might catch fire in the six months between now and the first nominating events – the Iowa caucuses and the New Hampshire primary.

But Clinton, the former first lady and ex-U.S. senator from New York, remains the front-runner despite her vulnerabilities. And she is trying to solidify her position and increase her likability with an unusually early ad buy costing an estimated $2 million. The Clinton campaign is running two 60-second TV ads to court voters in Iowa and New Hampshire by portraying Clinton as a champion of American families. The ads refer to Clinton's commitment to public service and how she was inspired by her mother, who overcame abandonment as a child. "We're going to make sure everyone knows who Hillary Clinton really is – who she fights for and what has motivated her lifelong commitment to children and families," Robby Mook, her campaign manager, told reporters. "Since Day One, we've planned for a competitive primary with Hillary herself working to earn every vote and, ultimately, the nomination."