ANALYSIS — Republicans are riding high after a series of redistricting victories that could help the GOP become the first party since 1978 to retain control of both chambers of Congress in a midterm election while holding the White House.

But two batches of Republican surveys show how such an outcome would still be tough to pull off, particularly in the House, and they provide some key lessons about polling along the way.

In late April, Punchbowl News reported on a batch of surveys from nine House districts conducted in mid-March by Ragnar Research Partners for Conservatives for America, which is connected to the Republican Study Committee in the House.

On a superficial level, the results might have looked like good news, considering GOP incumbents led in all but one of the polls. But a closer look showed warning signs for Republican chances of maintaining control of the House.

Only one of those districts is at or near the center of the House battleground. GOP Rep. Juan Ciscomani’s reelection race in Arizona’s 6th District is rated a Toss-up by Inside Elections, while three are rated as Lean Republican (Iowa’s 3rd, Michigan’s 4th and Virginia’s 1st), two are rated Likely Republican (Colorado’s 3rd and North Carolina’s 14th) and three are rated Solid Republican (Minnesota’s 1st, North Carolina’s 10th and Wisconsin’s 1st).