TN-Sen: Dem Phil Bredesen extends his lead over GOP's Marsha Blackburn, new poll shows

President Donald Trump won all but three of Tennessee's 95 counties en route to his victory over Hillary Clinton in the 2016 presidential election, and he remains highly popular there today.

Conventional wisdom says that the candidate he endorsed for the U.S. Senate seat, Republican Rep. Marsha Blackburn, would handily win over her Democratic opponent, former Tennessee Gov. Phil Bredesen. However, it's looking increasingly difficult for Republicans to hold on to the crucially important Senate seat.

Recent polling has not been friendly to Blackburn — and a new poll from CNN confirms the bad news.

What does the poll show?

Bredesen holds a 5-point lead over Blackburn among likely voters, 50 percent to 45 percent, the poll shows. When surveyed more broadly among registered voters, Bredesen's edge jumps to 8 points over Blackburn, 50 percent to 42 percent.

Unfortunately for Blackburn, a vast majority of likely and registered voters say they will not change their candidate preference before Election Day.

Overall, 84 percent of likely voters told CNN their mind is set on who they will vote for come November, while 78 percent of registered voters responded likewise. Just 20 percent of registered voters and 15 percent of likely voters admitted they are open to being swayed toward one candidate or the other.

CNN's poll marks the first major survey that shows Bredesen has extended his lead outside of a poll's margin of error. This is significant because it signifies that Bredesen has cemented a reliable lead with just weeks to go before the Nov. 6 election.

The survey shows Bredesen's lead, as found by an NBC News/Marist poll earlier this month, has expanded. The NBC News poll showed Bredesen with a 2-point margin over Blackburn among likely voters, 48 percent to 46 percent. However, the lead was within the survey's margin of error.

Is there any good news for Blackburn?

Apart from being firmly onboard with the "Make America Great Again" agenda in a vast pro-Trump state, a recent Fox News poll showed Blackburn with a 3-point edge over Bredesen among Tennessee likely voters, 47 percent to 44 percent.

However, that poll may be slightly biased because 53 percent of its likely voter respondents identified as Republicans while just 35 percent identified as Democrats. The remaining 12 percent did not identify with either party.