The phrase "a string of weakening" is correct and usable in written English.
It can be used to describe a series of events, actions, or statements that lead to a reduction in strength or effectiveness.
Example: "The team's performance has been marked by a string of weakening strategies that failed to deliver results."
Alternatives: "a series of declines" or "a chain of deterioration."
Before that, the FARC, which once controlled large areas of the country, had suffered a string of setbacks that severely weakened it and raised questions of how long it could keep fighting.
Senator Mitch McConnell is introducing a string of amendments that would weaken the bill.
He must also rebuild the New York branch, which has been weakened by a string of high profile departures, at a time when the industry is suffering one of its worst slumps in a decade.
Spain's Socialist government contends that ETA, whose name stands for Basque Homeland and Liberty in Basque, has been severely weakened by a string of arrests, but the group has staged more than a dozen attacks and killed two people since the beginning of the year.
The party has been buffeted by a weakening economy, and a string of controversies and blunders in recent weeks.
The party's loss of a string of regional elections over the past year has weakened Mrs. Merkel's center-right government and its overall standing in the polls.
Knightley said a string of business surveys sugested hiring intentions had weakened substantially in the period after the referendum on 23 June.
The debilitating effects of days of airstrikes by U.S., French and British forces are evident on the ground, as a lightly trained rebel force appears to be steadily retaking a string of strategic coastal towns from Gaddafi's weakened military.
It detected such a link in Africa (though there have been arguments about its methods, and a string of relatively conflict-free years after the period examined weakens the effect).
Since returning to the Kremlin, President Putin has signed a string of laws apparently designed to stamp out dissent and weaken civil society, including tougher punishments for unsanctioned protests and legislation which broadens the definition of state treason.
