The war in Iraq 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 Harry Reid of Nevada, 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 George W. Bush’s term. “This is 2006 2.0,” said Rahm Emanuel, who in 2006 was an ambitious Democratic House member from Illinois and Mr. Bush’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. Exceeding expectations that year, Democrats picked up six seats in the Senate, taking control of the chamber. In the House, where the Republican majority seemed to have exhausted itself after a dozen years, Democrats gained 31 seats and installed Nancy Pelosi, who is now retiring, as the first woman speaker. Mr. Bush, another victim of the six-year presidential itch, famously branded the outcome “a thumping.”

This year, the Senate map is stacked against Democrats — they would need to win at least four Republican-held seats to take control, all but one of them in states that Mr. Trump won in 2024. And not all of the most competitive races have gone as party leaders had hoped. But Democrats have benefited from some political twists in places where they had not anticipated being competitive, such as in Ohio, where Mr. Trump’s primary endorsement of the state’s attorney general, Dave Yost, over Senator Sherrod Brown, put that seat in play. The nonpartisan Cook Political Report on Thursday moved its ratings of the Ohio and Pennsylvania Senate races from leaning Republican to a toss up, underscoring the expanding battleground that Democrats would need in order to replicate 2006. Democrats say that they believe they are also increasingly competitive in other states carried by Mr. Trump two years ago, including Florida. While clear similarities exist this year, significant differences are present as well — not the least of which is that Americans consume and process political content far differently than they did 20 years ago, with an emphasis on digital media rather than traditional television advertising. Other structural changes have taken place that could influence the results. The two parties this year engaged in a redistricting war that could help stem some of the House losses Republicans might have suffered in a midterm year that traditionally runs against those in power. Polarization runs deeper, making it harder to shake voters from their party identification. Mr. Trump’s hold on his base seems stronger than Mr. Bush’s was in 2006, though it is potentially weakening amid a backlash to the war with Iraq. In the Senate and the House, the Democratic establishment did not get its preferred candidates through the primaries in some key races, including in Arizona and Georgia. And the rise of far-left socialist candidates has Republicans seeing an ope...