(CNN) - As Mitt Romney prepares to unveil his running mate pick Saturday morning, recent polls show President Barack Obama has expanded his margin over the presumptive GOP nominee.
According to a CNN/ORC International survey released Thursday, 52% of registered voters say they would support the president, while 45% are backing Romney.
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In the same survey last month, Obama held a three-point margin over Romney, 49%- 46%, a difference that fell within the survey's sampling error.
The results are in line with three other surveys released in the last two days. CNN's Poll of Polls, which averages the most recent results, indicates Obama is ahead with 49% support, followed by Romney at 43%.
Romney has also been struggling to improve his popularity among voters in recent weeks, with polls showing that the Republican candidate's unfavorability ratings are on the rise.
His unfavorability rating jumped from 42% last month to 48% now. Meanwhile, the president's 56%-42% favorable-unfavorable rating changed little during the same time period, according to the new CNN/ORC International poll.
The former Massachusetts governor has been dogged by attacks from the Obama campaign and its allies this summer over Romney's financial portfolio, as well as his tenure and business record at his former private equity firm, Bain Capital. In turn, the Romney campaign has also engaged in repeated negative attacks against the president.
Starting Saturday, the presumptive GOP nominee will blaze through the battleground states of Virginia, North Carolina, Florida, and Ohio on a four-day, high-profile bus tour.
- CNN Political Editor Paul Steinhauser contributed to this report.