Susan Page

USA TODAY

In what could be good news for endangered Republican senators up for re-election this fall, a majority of Hillary Clinton supporters say they are likely to split the ticket — that is, vote for the Democratic presidential candidate but then support some GOP candidates for the Senate or other offices down the ballot.

In a nationwide USA TODAY/Suffolk University Poll, a third of Clinton's supporters, 32%, say they are "very likely" to split their votes, and another 20% say they are "somewhat" likely. Twenty percent say they are "not very likely" to split the ticket, and 23% say they'll vote for Democratic candidates up and down the ballot.

In contrast, a majority of Donald Trump supporters say they probably or definitely will vote only for Republicans. A third, 33%, say they plan to vote a straight GOP ticket up and down the ballot, and another 20% say they are "not very likely" to vote for Democratic candidates for other offices.

The survey of likely voters, including 483 Clinton supporters and 409 Trump voters, has margins of error of +/-4.5 percentage points and 4.9 points for the partisan subsamples.

Poll: Fear, not excitement, driving Clinton and Trump supporters

USA TODAY analysis: Rich Democrats surge past GOP in political giving

The findings could raise the hopes of Republican Senate candidates in competitive contests in swing states, among them Florida, Illinois, Nevada, New Hampshire, North Carolina, Ohio, Pennsylvania and Wisconsin. Continued Republican control of the Senate could depend on GOP candidates convincing independent and Republican-leaning voters who decide to back Clinton to also cast a ballot for them.

The voters most likely to say they are very likely to split their votes include self-described moderates (41%), those with annual household incomes above $100,000 (41%), residents of the Northeast (38%) and Hispanics (37%).

The voters most likely to vote a straight party line include African Americans (42%), Republicans (37%), and those who describe themselves as "very conservative" (36%).