A safe Senate seat is a wonderful thing to have, right up until it requires a presidential rescue visit. Then it becomes a very secure chair with a helicopter circling overhead.

AP reports that Trump plans a Monday rally in Mississippi for Republican Sen. Cindy Hyde-Smith. She remains the favorite, but Democrat Scott Colom has mounted a serious challenge and outpaced her fundraising. Senate Democrats’ super PAC has put $1.2 million into the race. Mississippi is a state Trump won three times by an average of nearly 20 points.

This is not a prediction of an upset. It is an appreciation of the difference between declaring the house perfectly sound and spending the last week of the campaign checking why the floor is making that noise.

The useful thing about an expanded battleground is what it does to the people who thought the boundaries were permanent. Suddenly a voter becomes someone to persuade rather than a reliable feature of the scenery. A candidate might have to explain the job. A party might have to spend money defending a place it had mentally filed under ours, next question.

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That is healthy. A Senate seat belongs to the people who vote for it, an inconvenient ownership arrangement for anyone who has already picked out the curtains.

Of course, the president can help a candidate. He can also make the visit a reminder of whose party she represents. The rescue vehicle arrives carrying the brand. If voters’ problem is with the brand, a larger logo is an interesting repair strategy.

Democrats still have to win actual votes. A check is not a ballot, a promising map is not a result, and a Republican defending home turf is perfectly capable of defending it successfully. Enthusiasm should bring comfortable shoes, not a prematurely printed victory banner.

But the next time someone calls a seat safe, ask who it is safe from. Competition is supposed to be one of the features.

The chair can wait. The voters get to decide who sits down.