All year, political analysts and strategists have pored over the details of polling results showing the potential gap between the two parties in November's U.S. House elections fluctuating between a low single-digit Democratic advantage and a double-digit one.

Now, three months before Americans vote, two respected nonpartisan organizations see the Democratic trend solidifying. The Cook Political Report's David Wasserman said Democrats are "substantial favorites" to capture the House, while Larry Sabato's more cautious Crystal Ball rated them for the first time "a little better than 50-50" to regain control.

A Democratic takeover would transform Washington with increased pressure on President Donald Trump to compromise, greater oversight of his administration and, depending on events, a possible impeachment effort.

One of the most positive Democratic signs is their consistently strong showings in special elections for vacated House seats. Another looms next week in central Ohio, the last such test before the entire nation registers a judgment on Trump's first two years.

In nine special congressional elections since he became president, Democrats outpolled their party's base strength by an average of 8 points, according to Wasserman. A similar gain could enable Democrat Danny O'Connor to defeat Republican Troy Balderson on Aug. 7 in a district Trump won by 11 points in 2016 and would likely foretell a Democratic House.

In those earlier special elections, Democrat Conor Lamb won a longtime GOP House seat in Pennsylvania and Democratic challengers cut Republican margins sharply in seven other races. The size of the gains roughly resemble those before the 2006 election, the last time Democrats took the House from the Republicans. They'll need that big a national swing, because Republican-controlled redistricting in several states has solidified the GOP majority since 2010.

Another good signal is Democratic fundraising. Recent statistics showed that challengers outraised Republican incumbents in 36 of the 40 districts the Cook Political Report rates as the most competitive in November, though some GOP lawmakers have more cash on hand.

That includes three in Texas: the 7th in the Houston area, the 23rd west of San Antonio, and the 32nd in the Dallas area. In all three, changing population trends have narrowed the inherent advantages for Reps. John Culberson, Will Hurd and Pete Sessions.

Democrat Colin Allred (left) is challenging Republican U.S. Rep. Pete Sessions in the 32nd Congressional District. (Photos by Andy Jacobsohn / Staff Photographer)

In Texas, as well as elsewhere, Democrats have generally succeeded in nominating candidates whose views fit the districts they hope to represent, notwithstanding the highly publicized primary victories of a Democratic Socialist in New York and a few strong liberals elsewhere.

Most are stressing traditional economic issues like health care and playing down the prospect a Democratic House could seek Trump's impeachment. They hope to benefit from anti-Trump sentiment evident in polls showing greater enthusiasm about voting among Democrats and favoring candidates who would challenge him.

Many Republicans, meanwhile, are echoing Trump in stressing issues like immigration and crime in hopes of spurring the greater enthusiasm among their troops needed to maximize GOP turnout.

A comparable debate is occurring in the Ohio race to replace longtime GOP Rep. Pat Tiberi, who resigned from the seat he won in 2016 by better than 2-to-1. Pre-election indicators suggest a close outcome; two recent polls showed Balderson slightly ahead, but The Columbus Dispatch said Democratic absentee ballot requests and early voting are double the rate among Republicans, a reversal from 2016.

Another problem Republicans face nationally is that independents who voted for Trump are trending back to the Democrats. The most recent NBC News/Wall Street Journal Poll showed independents favoring Democratic congressional candidates by more than 20 points.

Meanwhile, the battle for the Senate is tightening. Until now, most analysts have agreed the fact that 10 Democrats are seeking re-election in states won by Trump will give Republicans enough victories to at least maintain — and possibly expand — their current 51-49 makeup.

But last week, Sean Trende, an analyst for Real Clear Politics, tweeted "Democrats no worse than 50-50 to take over the Senate." Others remain skeptical.

Polls show Democrats close or leading for three Republican-held seats, in Arizona, Nevada and Tennessee. And most Democratic incumbents in those 10 Trump states are at least holding their own, if not ahead. A new analysis by Republican strategist Bruce Mehlman suggests they may be less vulnerable than thought. In past midterm elections, his study noted, 90 percent of incumbents survived in states the other party carried in the prior presidential election

Meanwhile, Trump says he'll campaign virtually nonstop this fall for GOP candidates. That could increase Republican enthusiasm and Democratic turnout. Many crucial House races are in suburban areas where Hillary Clinton won in 2016 and Trump is more unpopular than nationally.

One thing is certain: the 116th Congress and Washington will look a lot different from the Republican-controlled 115th Congress. Next week's Ohio race may give another signal how different.

Carl P. Leubsdorf is the former Washington bureau chief of The Dallas Morning News and a frequent contributor. Email: carl.p.leubsdorf@gmail.com

What's your view?

Got an opinion about this issue? Send a letter to the editor, and you just might get published.