(CNN) Hillary Clinton has been sitting back and just watching Donald Trump do his thing. With Republicans openly defecting from the GOP nominee and polls showing that Trump is performing poorly in solidly red states like Georgia , as well as swing states like Pennsylvania and Ohio, there will be a strong temptation for Clinton to remain silent. No need to enter the fray when your opponent appears to be fraying by the seams.

But it would be a big mistake for Clinton to take this path forward.

The truth is that complacency is the enemy of political success. At a minimum, if there is a major domestic or foreign policy crisis that fundamentally shakes up the electorate, Trump's standing might quickly improve. As a Democrat who experienced the financial meltdown of 2008, which occurred right in the middle of the presidential campaign, she must know this first-hand.

If such a crisis occurred again, it would be important for voters to have a good sense of what kinds of issues and policies Clinton stands for to push back against any surge in Trump's standing. Providing voters with a strong sense of her vision will also be important if she wants to create greater distance between herself and Trump in states such as Florida, where the polls still show an extremely tight race.

Just as important is the fact that campaigns are not only about what happens in November, but also about preparing for the months that follow the inauguration. If Clinton is victorious, the reality is that at best she will have an extremely short time frame for securing legislation, as all new presidents discover.

The best-case scenario for Clinton would be that Trump's impact on the ticket is so detrimental that it produces reverse coattails, giving Democrats control of the White House and Congress. More likely, a Clinton victory would probably produce a Democratic Senate, with Republicans retaining control of the House. And, of course, Republicans might manage to preserve their control of both chambers, leaving Clinton with divided government.

With any of these outcomes, a Clinton presidency would be tough. Republicans would be determined to rebound from the Trump candidacy by preventing a Democratic president from making any legislative gains. Even in the best-case scenario, Senate Republicans would employ the filibuster to block the administration.

Just a couple of years later, Democrats could easily lose control of both chambers given the number of seats they want to defend (and, like in 1964, Republican districts that go Democratic because of a divisive presidential candidate would likely revert back to the GOP once he was off the ticket).

The most successful presidents enter the short window that a president enjoys to legislate after having articulated a broad vision of what they hoped to accomplish and what their key priorities would be.

When he ran for re-election in 1964, for example, Lyndon Johnson had made clear that he intended to pursue the civil rights revolution and to push for a series of bills that had eluded liberals for decades, including health care for the aged and federal assistance for secondary and elementary schools.

When Ronald Reagan stepped into the White House in 1981, most voters knew that cutting taxes and increasing military spending would be his top priorities. President Barack Obama came into office in 2009 having promised to restore the role of government in a nation that had been moving rightward since Reagan.

As a result of the economic crisis that unfolded in the middle of the campaign, he had shifted his legislative priorities to financial regulation and an economic stimulus. He did this while keeping his promise for finally dealing with health care.

Clinton has many strengths as a candidate. Her vast experience in Washington is about as formidable as we have seen in any recent campaign and her steely attitude in the face of vicious attacks should make Trump supporters worry. She has also done a good job since the summer at uniting a party that became badly divided during the primaries.

Too often, however, Clinton doesn't do enough to outline what she is fighting for and who she is as a leader. This vacuum of information is connected to why so many voters are often unwilling to trust what she says and often believe in the attacks against her character.

In the coming months, Clinton must do more to fill in the portrait that voters have of who she is as a politician. The time has come for Clinton to explain herself as something more than a winner and someone who knows how to get thing done. Voters need to know her vision of what the government should do to improve life of working Americans, what the role of the U.S. should be overseas and what political leadership means to her.

While many commentators thought that the Democratic convention did a good job starting to make this case, particularly the biographical film that highlighted her background, the conversation has come to a halt in recent weeks with Donald Trump once again moving front and stage with his controversial exploits.

Clinton has tended to sit back when things are going well. But these are the moments when she becomes most vulnerable. As tempting as it might be to watch Trump implode and make this election a mandate about him, she needs to persuade voters that she is ultimately the person they want in the White House or else she will start at a big disadvantage if she is victorious in November.

Clinton also has to be careful not to let the opportunity to attract Republican voters define her campaign. The message from the Democratic primaries was clear: Democratic voters want their candidate to stand for Democratic values. It will be important in the coming weeks to make clear that Clinton heard the message loud and clear.

Given the continued unease about her principles, this is not the time to make too many moves revolving around GOP voters rather than those of her own party.

Now, not later, is the time for Clinton to do the hard work of defining herself. That way, if she is indeed elected, her allies know what she will do, her supporters will be excited and prepared to mount a fight to achieve her goals in what will be a tough legislative environment -- and Republicans won't succeed when they try to define her in an unfavorable way.