Republican presidential nominee Donald Trump holds a rally with supporters in Kenansville, North Carolina, U.S. Sept. 20, 2016. Reuters/Jonathan Ernst

Presidential candidates Hillary Clinton and Donald Trump have only a few days left to prepare for the first debate Monday night, when the two major-party nominees will need to make a compelling case to voters in the key states that could decide who succeeds President Barack Obama in the White House.

The race to the White House often comes down to a handful of states, such as Ohio, Pennsylvania and Florida, that could swing the election. Democrat Clinton and Republican Trump will almost assuredly have these states in mind as they take to the debate stage Monday in Hempstead, New York.

The latest polls show Trump holds a small advantage in Ohio. The Real Clear Politics average put him up by 1.2 percentage points, while a poll last week from Suffolk University had him up by three points in the state. FiveThirtyEight's election forecast Wednesday gave Trump a 60.1 percent chance of winning the state.

Clinton has maintained a lead in Pennsylvania, however, where she has long held an advantage. The Real Clear Politics average had her up by a relatively comfortable 6.6 percentage points, while the FiveThirtyEight forecast gave here a 67.1 percent chance of winning the state in the general election.

Florida remains tight. In a two-person race between Clinton and Trump, the Real Clear Politics average pegs it as a tie. When third-party-candidate Libertarian Gary Johnson is included, Trump holds an edge of less than one percentage point in the state. The latest CNN poll in Florida found a 3-point advantage for Trump while the latest Monmouth poll found a 5-point lead for Clinton. The FiveThirtyEight forecast essentially has Florida as a coin flip, giving Trump a 55.2 percent chance of winning, with Clinton trailing at 44.8 percent.

Source: InsideGov | Graphiq

In other swing states, Trump holds a small lead in Nevada and in Iowa, while Clinton remains ahead in New Hampshire, Michigan and North Carolina.

All this means it's still really unclear who will be elected president in November. A recent CBS battleground poll that tracked registered voters across 13 swing states — North Carolina, Arizona, Colorado, Florida, Georgia, Iowa, Michigan, New Hampshire, Nevada, Virginia and Wisconsin — found a tie between Clinton and Trump. Each candidate garnered 42 percent support overall among voters in these states.

Overall, Clinton holds a 1.2 percentage point lead over Trump nationally, according to the Real Clear Politics average of polls. The FiveThirtyEight forecast Wednesday gave Clinton a 57.1 percent chance of winning the general election, while Trump had a 42.9 percent chance.