U.S. House Republicans have closed their 18-month investigation of Solyndra LLC’s loan guarantee after issuing three subpoenas, conducting five hearings and reviewing than 300,000 documents. Now, the issue lives on in the presidential campaign.

Backing fledgling companies such as Solyndra, which received a $535 million loan guarantee before it collapsed two years later, already has become a feature in political attack ads. Republicans and allied groups have used Solyndra as a metaphor for what they see as President Barack Obama’s broader failure to revive the economy.

“Solyndra is President Obama’s baby,” said Benjamin Cole, a spokesman with the American Energy Alliance, an industry- backed lobbying group that says it supports free-market principles. “He raised it, nursed it with the milk of taxpayer dollars and now avoids any claim to paternity.”

The alliance, which in March featured Solyndra in an ad critical of Obama’s energy policies, plans to raise it during a five-week bus tour in the U.S. to promote fossil fuels.

Solyndra is “a critical component” to explain to voters why “Obama’s energy policies have failed,” Cole said.