(CNN) -- As Sen. John McCain prepares to promote free trade during a high-profile trip to Colombia and Mexico, a poll out Tuesday suggests the issue may be a political hurdle as the general election campaign heats up.
Sen. John McCain's free trade stance could pose a problem in November, according to a new poll.
According to the CNN/Opinion Research Corporation poll, 51 percent of Americans view foreign trade as a threat to the economy -- the first time in a CNN poll that a majority of Americans report holding negative views on free trade.
That compares with only 35 percent of Americans who felt free trade posed a threat to the economy in 2000, and 48 percent who felt it was a threat in 2006.
Now, only four in 10 Americans say free trade presents an opportunity for economic growth, a sentiment that clearly makes the issue a challenge for McCain, especially in the crucial Rust Belt states most affected by the loss of manufacturing jobs over the last decade.
"It's possible that John McCain's decision to highlight his free trade position may wind up losing him some votes among Americans who feel threatened economically by competition from other countries," CNN polling director Keating Holland said. "Recent polls in states like Pennsylvania and Michigan have shown McCain well behind Barack Obama. Calling attention to his stand on an issue like trade may be a part of the problems he apparently faces in those Midwestern states."
The poll also shows that some of the key voting blocs McCain is courting are most against free trade. Women, older Americans and lower-income voters report feeling the biggest threat from unfettered trade.
Many of these voters were particularly receptive to Sen. Hillary Clinton in key states during the Democratic primary as she increasingly developed an anti-trade stance.
The survey results come as McCain, who is a strong supporter of the North American Free Trade Agreement, heads to Colombia and Mexico to promote the advantages off a free trade policy and economic cooperation. He made a similar trip to Canada earlier this month.
Campaigning Monday through Pennsylvania -- one of the crucial political battleground states most affected by the loss of manufacturing jobs -- the presumptive Republican presidential nominee acknowledged many voters disagree with him on the issue.
"I understand it's very tough. But for me to give up my advocacy of free trade would be a betrayal of trust," he told reporters Tuesday. "And the most precious commodity I have with the American people is that they trust me."
In another challenge for McCain, the new CNN survey indicates Americans continue to rank the economy as the most important issue in deciding their vote for president.
Nearly six in 10 voters say the country's poor economic conditions will be extremely important -- ranking the economy as the No. 1 issue in this campaign out of 15 issues tested in the poll.
That finding represents a clear change from the beginning of this year, when the war in Iraq and the economy were tied as the top campaign issues. Now, the economy is eight points ahead of Iraq -- a fact that could pose a threat to McCain, who has admitted he is more comfortable discussing foreign policy issues than economic ones.
Rising gas prices are also among voters' concerns, with nearly 50 percent saying the issue will play an important role in their vote for president. That number is just behind those that say the economy and Iraq are important, a clear sign that higher prices for gasoline are the primary reason for voters' economic worries, though not the only one.
"It also means that a significant number of voters are concerned about other economic woes, like the stock market or unemployment, rather than gas prices," Holland said. "Unless there is a noticeable upturn in the country's economy between now and November, this election is likely to be dominated by economic concerns."
The poll, conducted June 26-29, surveyed 906 registered voters and carries a margin of error of plus or minus 3.5 percentage points.