WASHINGTON — The U.S. Chamber of Commerce is weighing a major role in Democratic primaries in key congressional races nationally, which could produce weakened nominees who would be more easily defeated by Republicans, according to an internal memo obtained Thursday by The Associated Press.

The unorthodox strategy could heighten Democratic upheaval in battleground states such as Florida and Pennsylvania, where the party is struggling to unite around a nominee as it fights to retake the Senate — and that appears to be precisely the Chamber’s goal. It comes as the business lobby already has begun spending aggressively more than a year before the 2016 elections on behalf of select Republicans in the Senate, where the GOP is fighting to hang on to its newly won majority.

In addition, the Chamber’s memo has identified Republican House seats that have potentially vulnerable incumbents, including Maine’s U.S. Rep. Bruce Poliquin, R-2nd District.

Two Democrats — Emily Cain and Joe Baldacci — already have announced they’ll compete for the chance to take on Poliquin in Maine’s 2nd Congressional District race. Cain lost to Poliquin in 2014 but quickly regrouped for another match.

Republicans must defend seven Senate seats in states President Barack Obama won in 2012, and major clashes are shaping up with Democrats just as determined to snatch back the four or five seats they need to retake Senate control. The electorate could favor Democrats because more young voters and minorities turn out in presidential election years.

The memo was written by the Chamber’s top two political officials, Rob Engstrom and Scott Reed, to members of the Chamber’s Public Affairs Committee, a group of around 35 business leaders and others who will meet this fall to discuss political strategy and spending for the upcoming elections.

It lists four Senate races and five House races in which “intense Democratic primaries could significantly impact candidates moving into the general election,” urges committee members to study them closely, and concludes: “In the past, Democrats have been successful in places like Missouri by playing in GOP primaries. … In 2016, the political environment appears to be shifting.”

A senior strategist with knowledge of the deliberations, who spoke on condition of anonymity to disclose internal discussions, confirmed that the memo’s intent was to encourage involvement in the Democratic primaries, including possible spending on television ads. A weakened Democratic nominee in a state such as Florida or Illinois could make the general election much more winnable for the Republican candidate in the fall and require Democratic expenditures that could cut into the party’s budget elsewhere.

The approach builds on the Chamber’s successful decision in the 2014 election cycle to insert itself into more than a dozen GOP primaries on behalf of the most viable and business-friendly candidates. That helped Republicans avoid nominating embarrassing and inexperienced candidates who went on to lose to Democrats, as had happened in 2010 and 2012.

The Senate races the memo lists are:

• Illinois, where incumbent Republican Mark Kirk is highly vulnerable to a challenge from Democratic Rep. Tammy Duckworth. Duckworth is the establishment choice but is being challenged by former Chicago Urban League leader Andrea Zopp.

• Ohio, where Republican incumbent Rob Portman, a Chamber favorite, faces former Gov. Ted Strickland, a strong contender who nevertheless is being challenged by Cincinnati Councilman P.G. Sittenfeld.

• Pennsylvania, where Republican Pat Toomey is running for re-election against former Rep. Joe Sestak, whose reputation for erratic campaigning sent Democratic leaders to recruit another Democrat, Katie McGinty, former chief of staff to the governor.

• Florida, where Republican Sen. Marco Rubio is running for president. Democratic leaders hoped to unite behind Rep. Patrick Murphy, but liberal firebrand Rep. Alan Grayson upset their plans. Republicans face problems of their own in that race with numerous candidates running, but facing Grayson rather than Murphy would improve their prospects.

On the House side, Republicans are unlikely to lose their large majority, but the Chamber seems determined to keep it that way. The memo lists five races where Democrats might not have a clear shot for a nominee to take down a potentially vulnerable Republican incumbent: Poliquin in Maine; Bob Dold in Illinois, Cresent Hardy in Nevada, Mike Coffman in Colorado and Martha McSally in Arizona.