Senator Corker, whose seat Ms. Blackburn would like to fill, called the Trump-era Republican Party “cultish.” Ms. Blackburn is firmly in the cult. She was one of 15 House Republicans who signed a letter nominating Mr. Trump for the Nobel Peace Prize before he ever met with the North Korean leader Kim Jong-un, a move that seems premature in the wake of the duo’s Singapore meeting. She was an early primary supporter of Mr. Trump in 2016, and even floated herself as a vice-presidential option.

But as with any cult, membership may bring praise from the leader, but it will also create awkward situations when dealing with the outside world. When Mr. Trump announced tariffs on steel, the state’s auto industry braced for the impact. Mr. Corker and Lamar Alexander, the state’s senior senator, were quick to denounce the move, but Ms. Blackburn could only waffle, saying she was “waiting to see” the plan. Tennessee’s automakers and suppliers are a potent force in the state economy, responsible for 135,000 jobs and 830,000 vehicles in 2016. If tariffs start to dig into their profits, they won’t stay silent — and Ms. Blackburn, as the local voice of the Trumpist Republican Party, will bear the brunt of their criticism.

A week after the tariff announcement, the news blew up around the Trump administration’s policy of child separation for undocumented immigrants. Mr. Corker slammed the change in direction from the Obama and Bush years, saying that children “should be protected and not used for deterrence.” But Ms. Blackburn followed the president’s line that Democrats were to blame. “We are in this position because liberals would not pay to enforce our immigration laws,” she said. It was only days later, after the president himself indicated he might change the policy, that Ms. Blackburn said the process had to end.

Just one day later, a government report calling for the sale of government assets, including Tennessee Valley Authority transmission lines — considered sacrosanct by Tennessee voters — forced Ms. Blackburn to attempt to distance herself from the president yet again. But few people are buying it: A candidate who has promised to do everything to implement the president’s agenda is not very convincing when she tries to walk away from the specifics.

Obviously, there are a lot of voters who will support Ms. Blackburn as long as she supports the president — he won Tennessee by 26 points. But for the rest, Ms. Blackburn is creating a huge opening for her Democratic opponent, former Governor Phil Bredesen, to not just capture the center but to also peel away a few conservatives by positioning himself as the real defender of the state’s interests.