WASHINGTON — Senator Elizabeth Warren set off a new round of speculation about her presidential ambitions last week by sparking a liberal rebellion against a spending bill, as outside groups stepped up an effort to draft her.

Warren, a Massachusetts Democrat, often answers the question in the present tense — “I’m not running” — which leaves room for her to change her mind.

In an interview that aired Monday on National Public Radio, she was pressed several times about her use of the present tense. After saying again that she is not running, she added another flourish she sometimes uses: “You want me to put an exclamation point at the end?”