HARRISBURG, Pa. (KDKA/AP) – The first debate is set for Monday for Republican U.S. Sen. Pat Toomey of Pennsylvania and his Democratic challenger, Katie McGinty, in an increasingly nasty race that could decide whether the GOP hangs onto its Senate majority.

Toomey said he will seek to highlight differences, including on national security and his record of fighting against tax increases.

“Katie McGinty has spent her professional life raising middle class taxes, or trying to raise middle class taxes, and if there’s anybody in the Congress that’s been fighting against higher taxes, that’s me,” Toomey said Friday.

McGinty has said she opposes a middle-class tax increase and has criticized Toomey in recent days over his refusal to disavow the GOP’s presidential nominee, Donald Trump.

The editorial board of Pennsylvania’s largest newspaper, The Philadelphia Inquirer, endorsed McGinty on Sunday, saying McGinty “has a genuine grasp on the human consequences of government policies and seeks to improve the quality of life for all.”

Differences over gun rights, abortion and immigration are also prominent issues in the campaign.

The hour-long debate will be taped at 1 p.m. in the KDKA-TV studios and will be broadcast at 7 p.m. It will be made available to stations in other media markets.

KDKA’s Money and Political Editor Jon Delano tells the “KDKA Morning News” the Pennsylvania Senate race is “critical” to which party controls a majority.

“Most analysts nationwide say that this race for control of the United States Senate now comes down to perhaps four to eight states…Pennsylvania is one of those eight possible states that could go either way, so a debate like the one we are having on KDKA-TV tonight is absolutely critical to both candidates in these waning days of this campaign,” Delano said.

The pair is scheduled for a second and final debate Oct. 24 in Philadelphia. The election is Nov. 8.

The first-term Toomey is among the Senate’s most endangered Republicans, running for re-election in a state where registered Democrats hold a four-to-three advantage over Republicans.

Toomey is backed by business associations and anti-tax and anti-regulation activists, including the U.S. Chamber of Commerce, the American Bankers Association, conservative billionaires Charles and David Koch and the Washington, D.C.-based Club for Growth, where he was president before running for Senate.

Toomey is ranked by the American Conservative Union as the third-most conservative Pennsylvania member of Congress and 13th among U.S. senators. A former investment banker and restaurateur, Toomey also served three U.S. House terms.

McGinty is popular with labor unions and environmental advocacy organizations, and had the backing of the Democratic Party’s power structure to help her win a four-way primary. She got her start in government working for then-U.S. Sen. Al Gore of Tennessee. She later worked for Bill Clinton’s White House and two Pennsylvania governors, Ed Rendell and Tom Wolf.

She ran for governor in 2014 and finished a distant fourth in a four-way primary. She has endorsed Hillary Clinton for president and hews closely to Clinton’s policy positions.

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(TM and © Copyright 2016 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2016 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)

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