Most polls show Hillary Clinton defeating Donald Trump in a presidential contest, but a new survey indicates that in such a matchup, more Democrats may cross party lines than Republicans.

A poll released by Mercury Analytics, a Democrat-run firm with clients including Fox News and MSNBC, found 19 percent of likely Democratic voters said they'd consider bucking their party and vote for Trump, while just 14 percent of GOP voters said they might do the same for Clinton.

The company also found a much higher percentage of Democrats were "100 percent sure" of voting for Trump than Republicans considering voting for Clinton.

Mercury carried out the poll over the last week in order to gauge the effect of Trump's first television ad this week. It has a margin of error of plus or minus 3.5 percent.

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