(Reuters) - This year's election year battle for control of the U.S. Senate is intensifying, as voter disaffection for President Donald Trump's response to the COVID-19 pandemic weighs on a growing number of Senate races in the South and Midwest.
Republicans hold a majority of 53 seats in the 100-seat Senate. But the number of competitive Republican seats has grown to include one held by Senator Kelly Loeffler in Georgia and an open seat in Kansas, where long-time Republican Senator Pat Roberts is retiring.
Democrats would need to net at least three Republican-held seats for a majority, if Democrat Joe Biden wins the White House, giving his running mate Kamala Harris a tie-breaking Senate vote, or four seats if Biden loses.
Here is a look at 10 races where Senate Republican incumbents are locked in highly competitive contests against Democratic challengers, and two where Democrats are on the ropes:
Republican Senator Martha McSally lags Democratic challenger Mark Kelly in fundraising and trails him by an average of nearly 8 percentage points in opinion polls, according to the campaign tracking website RealClearPolitics.com.
McSally, a former U.S. representative and U.S. Air Force combat pilot, was appointed to the seat once held by the late Republican Senator John McCain after losing her 2018 Senate bid to Democrat Kyrsten Sinema. Kelly, a former astronaut and U.S. Navy combat pilot, has been leading McSally in opinion polls for more than a year.
Republican Senator Cory Gardner, a former U.S. representative who entered the Senate in 2015, is among the most vulnerable Senate Republicans partly because of his allegiance to Trump in a state that has gone Democratic in the last three presidential elections.
Democrat challenger John Hickenlooper, a former two-term governor and 2020 presidential hopeful, had more money than Gardner as the race entered its final months and now holds a double-digit lead in opinion polls, according to FiveThirtyEight.com.
First-term Republican Senator David Perdue, a wealthy businessman who promotes himself as a Trump ally, holds a razor thin lead over Democratic challenger Jon Ossoff, according to RealClearPolitics.com.
Ossoff, an investigative journalist and media executive, ran a powerful campaign for a U.S. House of Representatives special election in 2017 but ultimately lost. Democrats believe he could oust Perdue, partly as a result of public dislike for Trump's handling of the COVID-19 pandemic that has hit Georgia hard.
In an election fluke caused by the retirement of former Republican Senator Johnny Isakson, both of Georgia's U.S. Senate seats are up for grabs on Nov. 3.
Republican Senator Kelly Loeffler, who was appointed as Isakson's replacement last year, is running in a multi-party, multi-candidate "jungle primary" special election, featuring a powerful Republican opponent, Representative Doug Collins.
The contest is widely expected to end in a January run-off election. But as Loeffler and Collins battle each other for Republican votes, Democrat Raphael Warnock leads in the polls and had more cash on hand than either Republican as the race entered its final weeks.
Democrat Theresa Greenfield, an urban planner and real estate developer, is leading Republican Senator Joni Ernst by several percentage points on average at a time when Iowa has seen a record number of hospitalizations due to the coronavirus.
Greenfield has accused Ernst of being a rubber stamp for Trump and not taking the COVID-19 pandemic seriously enough. Ernst, who is also trailing Greenfield in campaign money, has sought to use her Senate Judiciary Committee role in U.S. Supreme Court nominee Amy Coney Barrett's confirmation process to appeal to conservative-leaning independents and Democrats.
Not since 1932 has a Democrat won a U.S. Senate seat in Kansas, one of the country's most reliably Republican states. But this year, Democratic state Senator Barbara Bollier and Republican Representative Roger Marshall are locked in a tight race for the seat of Republican Senator Pat Roberts, who is retiring.
With healthcare a leading issue in the COVID-19 pandemic, Marshall leads Bollier by only a single percentage point on average, according to RealClearPolitics.com. Bollier massively outraised Marshall, by $13.5 million to $2.9 million in the third quarter, and entered October with nearly $6 million more in cash.
Four-term Republican Senator Susan Collins, a New England moderate long known for her independence, has seen her popularity flag among voters amid criticism that she failed to be a moderating force in the Senate during Trump's presidency.
Her Democratic challenger, Maine House of Representatives Speaker Sara Gideon, leads Collins by several percentage points in opinion polls and has massively out-fundraised the Republican.
Republican Senator Steve Daines is running neck-and-neck against two-term Governor Steve Bullock, a former presidential candidate who has branded himself as an independent-minded Democrat. Daines, a former congressman and software executive, is known as a reliable conservative and has touted his ties to Trump.
Bullock was a late entry, jumping into the race in March. But he managed to raise funds quickly and now shows signs of building a small lead over Daines in opinion polls after trailing the Republican in recent weeks.
North Carolina has erupted into one of the most dramatic Senate races in the country, with Democrat Cal Cunningham's candidacy tripped up by a sex scandal after he had dominated the campaign for months.
Once among the Democratic Party's strongest Senate candidates, Cunningham has seen his double-digit lead over Republican Senator Thom Tillis erode to a single percentage point. But it is not clear whether a sex scandal in the age of Trump can fully overcome the tide of political polarization that has largely run against Tillis up to now.
Graham, one of Trump's closest allies in Congress, was last re-elected to the Senate in 2014 with more than 55% of the vote. But this year, he holds only a small lead over Democrat Jaime Harrison, who is running a powerful campaign backed by staggering fundraising numbers.
Recent polls suggest Graham may have moved into a slight lead over Harrison, based partly on his role in overseeing the confirmation process for Supreme Court nominee Amy Coney Barrett. Once seen as a Trump critic, Graham faces skepticism among conservatives over his recent conversion to Trump ally, while the loss of his former maverick persona has disappointed moderates, analysts say.
Democratic Senator Doug Jones, considered the most vulnerable Democrat in the Senate, won election to the seat that Republican Jeff Sessions vacated to become Trump's attorney general in 2017. In a state normally considered safe for Republican candidates, Jones bested former Alabama Supreme Court Chief Justice Roy Moore, whose campaign was snarled by allegations of sexual misconduct.
The Democrat now faces former Auburn University football coach Tommy Tuberville, a Republican who defeated Sessions' attempted comeback earlier this year. Tuberville has held a strong lead. But recent polling data suggests the race could be tightening, with Jones holding a cash advantage of more than $6 million over Tuberville in the final weeks.
Democratic Senator Gary Peters has a small lead over Republican challenger John James in a state that represents a major battleground in Trump's re-election bid.
The race leans in Peters' direction, according to analysts. But James, a Michigan businessman, has run a strong campaign, raising Republican hopes that he could score an upset victory over the incumbent on Election Day.
(Reporting by David Morgan; Editing by Scott Malone and Aurora Ellis)