With more than $200 million outside spending pouring in, the North Carolina Senate race has been the most expensive congressional race so far in 2020, followed by the Iowa and South Carolina Senate races, according to the Center for Responsive Politics’ analysis of campaign spending records.

In all of the 10 most expensive Senate races this year, Democrats have been vastly outraising and outspending Republicans, especially where Democratic challengers are competing against Republican incumbents. Meanwhile, big-money outside political groups from across the aisle have been driving up the spending.

Across the Senate battleground, North Carolina is a state that perhaps more than any other could ultimately tilt control of the chamber - reflected in a stunning $280 million in campaign money and outside money being poured into the state.

In the competitive race, recent polling shows Republican Sen. Thom Tillis trailing slightly behind Democrat Cal Cunningham. The candidates have spent more than $64 million in the contest, with Cunningham raising and spending more than twice the amount from Tillis, while outside groups across the board have spent upwards of $215 million supporting the two.

Similarly, the contest between Republican Sen. Joni Ernst and Democratic challenger Theresa Greenfield in Iowa has attracted far more spending from political interest groups than the candidates. The candidates’ campaigns have spent about $64 million so far, but outside groups have funneled at least $170 million into the race, with more than $94 million going into unseating the incumbent senator and more than $74 million spent to fend off the challenger.

South Carolina rounds out the top three, with more than $209 million being spent in a state that is surprisingly competitive this cycle for the Senate. The candidates have spent far more than outside groups though, with $164 million being spent by Democrat Jaime Harrison and GOP Sen. Lindsey Graham, compared to $45 million by outside groups. Harrison’s campaign, in particular, raised a whopping $107 million and spent $104 million of that by mid-October, compared to Graham, who raised $72 million and spent $60 million.

Arizona and Maine finish in the top five, with more than $208 million and $180 million spent in each respective race. Similar to South Carolina, the Arizona candidates’ campaigns -- Sen. Martha McSally and Democrat Mark Kelly -- have poured more money into the contest -- more than $125 million -- compared to outside groups at roughly $83.4 million.

In Maine, where outside groups are spending more than candidate campaigns, Democratic challenger Sara Gideon has raised and spent twice the amount Republican Sen. Susan Collins, but about the same amount of outside money has supported the two candidates.

-ABC News' Kendall Karson and Soorin Kim

ABC News Political Director Rick Klein breaks down the key states to watch in the battle for the White House and for control of the U.S. Senate.

At his third rally of the day -- the first of two in Michigan -- President Donald Trump spoke for over an hour and told supporters in Traverse City something that he has told each battleground state that he has visited which is that if he wins their state, he wins the whole thing.

"This is a -- this is a big important place. We -- if we win Michigan, it's over. It's over, we win the whole thing," Trump said. "Four more years and then we can finish the job we started so well. We can finish the job."

Pence spoke ahead of Trump and delivered a near-verbatim stump speech, although to a much larger than usual crowd for the vice president. Pence normally draws a few hundred supporters out at his rallies -- never anywhere close to the thousands of supporters that Trump draws.

-ABC News' Terrance Smith

As Americans are urged by election officials to return their absentee ballots as soon as possible, several states have begun reporting the number of mail-in ballots they have received to date.

Using data collected by the United States Elections Project, ABC News calculated the absentee ballot rate of return for 11 states deemed as competitive, and which also provide complete information on both absentee ballot requests, and the number of ballots returned.

This is the latest data analysis:

ARIZONA -- As of Nov. 2
Absentee ballots requested: 3,448,181
Ballots returned: 2,471,577
Rate of Return: 71.7%

*Arizona does not distinguish between mail ballots returned and early in-person votes.

FLORIDA -- as of Nov. 2
Absentee ballots requested: 6,004,485 
Ballots returned:  4,649,919  
Rate of Return: 77.4%

GEORGIA -- as of Oct. 31
Absentee ballots requested: 1,782,653    
Ballots returned:  1,223,123  
Rate of Return: 68.6%

IOWA -- as of Nov. 2
Absentee ballots requested: 1,002,273   
Ballots returned: 955,975
Rate of Return : 95.4%

MICHIGAN -- as of Nov. 2
Absentee ballots requested: 3,318,609  
Ballots returned:  2,841,696 
Rate of Return: 85.6%

MINNESOTA -- as of Nov. 2
Absentee ballots requested: 2,055,519 
Early vote: 1,716,675 
Rate of Return: 83.5%*

*Minnesota does not distinguish between mail and in-person ballots on their state reports. Thus, the statistics reported combine all in-person early and mail ballot votes.

NORTH CAROLINA - as of Nov. 2
Absentee ballots requested: 1,455,328   
Ballots returned: 937,895 
Rate of Return: 64.4%

NEW HAMPSHIRE -- as of Oct. 27
Absentee ballots requested: 225,002 
Ballots returned:  181,577  
Rate of Return: 80.7%

NEVADA -- as of Nov. 2
Ballots sent out to active registered voters: 1,768,994  
Ballots returned: 545,399 
Rate of Return: 30.8%

*Note: Every active registered voter in Nevada was automatically mailed a ballot this election. Historically, most Nevadans vote early in person. In 2016, for example, approximately 48% of Nevada active registered voters cast ballots during early voting and about 24% of active voters voted in person on Election Day. It seems that despite the mail ballots going out to all active voters, many are still opting to vote that way (though the mail turnout is much higher than usual -- only about 5% voted via absentee ballots in 2016).

PENNSYLVANIA -- as of Nov. 2
Absentee ballots requested: 3,097,640    
Ballots returned: 2,414,351
Rate of Return: 77.9%

WISCONSIN --as of Nov. 2
Absentee ballots requested: 1,421,390 
Ballots returned: 1,241,690 
Rate of Return: 87.4%

-ABC News' Arielle Mitropoulos