Joe Biden's campaign is worried that its supporters might become complacent in the concluding weeks of the presidential race. Therefore, it is reminding them that Donald Trump still has a chance of winning this race, despite trailing the former vice president in polls in several key swing states. It is expecting the race to come down to the wire.

Biden campaign manager Jen O'Malley Dillon released a memo to supporters over the weekend, noting that Trump can still end up winning this race. Dillon pointed out that every indication they have seen suggests the presidential race is likely to come down to the wire.

She went on to suggest that the race is closer than some of the predictions doing the rounds on social media and television. O'Malley Dillon also pointed out that Biden and Trump are still level-pegging in the key battleground states, where the Nov. election will be decided.

O'Malley Dillon also admitted that campaigns usually have motivations to keep supporters interested in the race, before noting that Biden is only leading in polling and according to some ongoing punditry on Twitter and TV. The recently published NPR/PBS NewsHour/Marist poll shows Biden leading by 54 percent to 43 percent nationally among potential voters.

Moreover, the Democratic nominee also leads Trump in several percentage points in key states, including Wisconsin, Michigan, and Pennsylvania, according to Real Clear Politics polling averages. The margins in places in North Carolina and Florida are relatively smaller.

Biden held a campaign rally in Durham, N.C., over the weekend, where the former vice president urged supporters gathered at a drive-in event to cast their votes. He also noted that the state's early voting period began on Oct. 15.

Trump's weekend also included campaigning, with the president making stops in Wisconsin and Michigan Saturday, before heading west. On Sunday morning, he visited a church in L.A. and held a rally in Carson City, Nev., later in the evening. On Monday, he will head to Arizona.

In her memo, O'Malley Dillon recalled that Trump ended up winning the Electoral College, even though he lost the popular vote, and polls showed Hillary Clinton as the favorite. She wrote that Trump's ability to make a comeback into contention during the concluding days of a campaign couldn't be underestimated.

Referencing a recent injection of a huge amount of money to pro-Trump super PACs, she noted that they could erase the Biden campaign's financial advantage with the stroke of a pen. She was probably referring to the $75 million cash infusion to Preserve America PAC by Sheldon Adelson and his wife, Miriam.