But Rubin promises that that message will remain at Warren’s core in the final two weeks.
In recent days, both candidates have begun holding large rallies. Brown appeared with Senator John McCain of Arizona over the weekend in Melrose. He is expected to hold events with a number of prominent Republicans in the coming days, including Governor Chris Christie of New Jersey on Wednesday.
The rallies appear to be be a larger part of Warren’s overall strategy. She drew sizable crowds in Worcester, Beverly, and Northampton in weekend events with Democrats, including Senator Al Franken of Minnesota and former senator Max Cleland of Georgia. The rallies are intended not only to raise Warren’s visibility, but also to motivate supporters.
Both candidate say they will have a strong get-out-the-vote effort, though Democrats have long held a significant advantage in the state.
Polls have shown the candidates are close, with Warren possibly holding a small lead.
The Warren campaign puts the number of undecided voters between about 6 and 12 percent, depending on whether the group includes voters who are leaning toward one candidate. Brown aides are less willing to discuss such calculations.
Warren’s team believes that a large majority of those voters plan to support Obama, making the case about Senate control particularly effective.
David Filipov of the Globe staff contributed to this report. Noah Bierman can be reached at email@example.com.