Last week, Donald Trump became the presumptive Republican nominee for president of the United States. The controversial front-runner's lead was cemented first by a resounding victory in the Indiana primary on Tuesday and second by the concessions of the two remaining contenders, Texas Sen. Ted Cruz and Ohio Gov. John Kasich, on Wednesday. Via Twitter, Republican National Committee Chairman Reince Priebus urged his party to rally around Trump.

As the Republican Party tries to pick up the pieces, Democrats may be tempted to start planning for an easy victory in 2016. And who can blame them? After all, a candidate from a splintered party who is short on policy proposals and high on insults for key demographic groups should be easy to beat. However, this election won't be the cakewalk that many Democrats are dreaming of, and the party should approach it with caution.

Democrats' first challenge continues to be Vermont Sen. Bernie Sanders. Although political observers generally agree that former Secretary of State Hillary Clinton will most likely be the Democratic nominee, Sanders continues to stay in the race. While Sanders' ongoing campaign doesn't seem to have prevented Clinton from acting like the nominee and formulating a strategy to defeat Trump, it does point to the division within the Democratic Party base. In any other year, that division might be fatal to the party's chances for the White House. This year, the GOP's even deeper divisions will help mitigate the fallout from the Clinton-Sanders divide, but the potential for damage is still exists. Though Clinton may cinch the nomination, she may not end up with the votes of Sanders' supporters in November. Those missed votes could diminish her chances of victory.

Editorial Cartoons on Donald Trump View All 455 Images

Another of the Democrats' challenges lies in Clinton herself. Although she carries with her the mantle of a historical candidacy and a resume that makes her significantly more qualified for the presidency than Trump, she also comes with a tremendous amount of political and personal baggage. How much the old Clinton scandals will come back to haunt her remains to be seen. Although Trump is trying to make them an issue, past controversies such as former President Bill Clinton's infidelities have already played out in the press several times over. However, the current FBI investigation into Hillary Clinton's use of a private email server while she was secretary of state continues to be a problem. It has been a distraction for her candidacy throughout the primary process and has no doubt dampened the enthusiasm of potential supporters.

Although Trump is hardly unmarred by scandals of his own, the fact that Clinton is still dogged by the email investigation prevents her from completely claiming the higher ground. As long as the investigation remains open, Clinton's innocence in the matter can be challenged. That situation is hardly ideal for any presidential candidate.

Finally, Trump himself presents a formidable challenge. His Republican primary opponents failed to recognize that, and they've since paid the price. Some of Trump's primary election advantages will be erased in the general. He'll be one of two candidates, not 17, and he'll be facing an opponent who is as well-known and as much of a media magnate as he is.

However, one of Trump's biggest advantages may remain intact: his ability to operate outside the rules of conventional wisdom. Since entering the Republican race, Trump has managed to stay on top despite committing gaffes that would have finished other candidates. His proposal for a border wall alone should have caused his exit from the race, and yet he stands today as the Republican nominee. Will general election voters hold him to a higher standard than Republican primary voters did? Hopefully. But if not, Democrats will find themselves at a disadvantage this fall.