Chris Pappas is stopping himself from getting too excited ahead of Tuesday’s midterm election.

“I take nothing for granted,” said the four-term US representative and Democratic nominee for New Hampshire’s open Senate seat. “This is a very purple, competitive state. Elections are never in the bag here.”

The race to replace the retiring Democratic senator Jeanne Shaheen has emerged as a source of 11th hour anxiety for the party.

In their attempt to gain four seats and reclaim control of the Senate, Democrats can’t afford to lose one they already hold. But September polling showing Pappas virtually tied with his Republican opponent, former senator John Sununu, rattled party strategists and raised the prospect that New Hampshire could become an unexpected battleground.

The warning signs were striking in a state Donald Trump has lost in each of his three presidential bids.

The blessing and curse of Trump’s shadow

While Pappas has regained a narrow advantage in most polls, and the Cook Political Report moved…