If Sanders cannot come out on top or at least garner more votes than Warren, there is not much of a path forward for him, Stirewalt claimed Monday on "The Daily Briefing."
"There's no way that the two of them -- they're not both coming out of New Hampshire," he said.
"Both represent neighboring states in the United States Senate. Both are well-known. Both have a claim to New Hampshire.
"There's no way that Bernie Sanders could lose New Hampshire or come in behind Elizabeth Warren and make an argument to go forward."
Looking closer at the lawmakers' bids, Stirewalt claimed both are laying claim to the "far-left vote" in the Democratic Party.
However, Warren is making a good argument for why those particular voters should coalesce around her bid, he said.
"Elizabeth Warren is making an increasingly effective pitch for those voters," he said.
"She's very plan-oriented. She makes an argument that she is more electable than Bernie Sanders."
He added Warren does not have the self-described "democratic socialist" label affixed to her as the Vermont lawmaker does, which makes her seem more electable.
At the same time, the pair's combined presence gives the current front-runner a continued level of comfort while the very-liberal vote is split amongst the two.
"As long as they're dividing the far-left vote in the Democratic Party, it makes it harder for them to take on Joe Biden," he said.