WASHINGTON — He was supposed to break through the congressional logjam. End the pandemic. Get the economy back on track. Days before he hits his one-year mark in office, a torrent of bad news is gnawing at the foundational rationale of President Joe Biden’s presidency: that he could get the job done. In the space of a week, Biden has been confronted by record inflation, COVID-19 testing shortages and school disruptions, and the second big slap-down of his domestic agenda in as many months by members of his own party.