With an unpopular war and high prices agitating voters, members of both parties see parallels to an election cycle when Democrats romped. But a lot has changed.

The war in the Middle East is increasingly unpopular. So is the president as his numbers dip perilously — a common development in the sixth year of a presidency. Congressional Republicans are embroiled in unsavory scandals. Americans are shelling out big bucks for gas while economic anxiety runs high.

The grim backdrop for November’s midterm elections has created a steep challenge for Republicans and opportunities for Democrats that look much the same as those they encountered in 2006. Back then, congressional Republicans faced the voters at the midpoint of President George W. Bush’s second term, with the public roiled by the war in Iraq, high fuel prices and a series of ugly accusations against members of the G.O.P. majority on Capitol Hill.

“It is striking,” said Senator Chuck Schumer of New York, the Democratic minority leader and chief architect of his party’s Senate campaign strategy this year and two decades ago. “The analogy is amazing.”

The parallels are not perfect, since politics and campaigns have both changed radically over 20 years. But the comparisons are instructive, as officials in both parties stare down the final months of an election that will determine who controls Congress for the remainder of President Trump’s term.

“This is 2006 2.0,” said Rahm Emanuel, who in 2006 was an ambitious Democratic House member from Illinois and Mr. Schumer’s counterpart across the Capitol as the head of the Democratic Congressional Campaign Committee. “The similarities are eerie.”

Mr. Emanuel and Mr. Schumer both have good reason to look back fondly on 2006, when Democrats triumphed in a blue wave.