Supporters look on as U.S. Rep. Marsha Blackburn (R-TN), Republican candidate for U.S. Senate, speaks to reporters after she cast her ballot during early voting at the Williamson County Clerk's office, October 31, 2018 in Franklin, Tennessee.

Rep. Marsha Blackburn will win her U.S. Senate race against Democratic former Gov. Phil Bredesen, keeping the Tennessee seat in Republican hands, NBC News projects.

The heated race, which some voters described as "vicious," pitted two household names in the state against each other after Republican Sen. Bob Corker announced his retirement. It was one of the rare Senate races where Democrats had hoped for a pickup as the GOP threatened to expand its majority in the chamber.

Blackburn focused her campaign message on supporting President Donald Trump's agenda in an effort to appeal to the state's dominant Republican constituency.

Nonpartisan political analysis site Larry Sabato's Crystal Ball had labeled the state as lean Republican and a recent NBC News/Marist poll showed Blackburn with a 4 point lead.

Tennessee hasn't had a Democratic U.S. senator since Jim Sasser was unseated by Bill Frist in 1994. Trump won the state by 26 points over Hillary Clinton in the 2016 election.

Due to the state's conservative bent, Bredesen, a former two-term governor, had to demonstrate that he would be able to break with his Democratic colleagues on certain issues. For instance, Bredesen endorsed Trump's second nominee to the Supreme Court, Brett Kavanaugh, despite the former D.C. circuit judge being accused of sexual assault. Kavanaugh has denied the allegations.

He also said he would not support Democratic Sen. Chuck Schumer if Democrats were to regain the majority in the Senate.

Immigration was a major factor in the race, especially as Trump railed about a caravan of migrants from Central America, located deep in Mexico but headed to the U.S. border.

Bredesen said in an interview with MSNBC's Kasie Hunt that it was "beyond belief" that anyone would label the caravan "as some sort of threat," to the United States.

Blackburn stuck with the president's hard line. She recently published an op-ed arguing that the caravan was tantamount to an invasion and a threat to the nation's security.

Millions of dollars in advertising money poured into the race. Billionaire and former New York City Mayor Mike Bloomberg hosted a fundraiser for Bredesen recently in Manhattan.

Outside groups spent just over $50 million on the race, including $7 million against Blackburn by a super PAC aligned with Schumer, and $13 million from the Senate Leadership Fund versus Bredesen.

The SLF is a super PAC backed by former associates of Republican Senate Majority Leader Mitch McConnell, R-Ky.