Most observers predict Democratic gains in the House this fall, but just how big is the Democratic advantage? A new set of measures from the inaugural Grinnell College National Poll shows that this lead is narrower than commonly understood — and that Democrats’ key advantage is the high level of engagement reported among the party’s voters.

Most polls ask respondents for which party they would vote on a generic House ballot. This question, which ignores the actual candidates in a race and the power of incumbency, leads to notoriously noisy results. Nate Silver’s FiveThirtyEight polling round-up shows everything from a 2- to 14-point advantage for Democrats on a generic ballot, depending on the poll and its methodology — the difference between Republicans narrowly holding the chamber and a Democratic landslide.

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Interpreting many of these polls is challenging because they report results from all registered voters, as opposed to just those likely to vote on election day.

The Grinnell College National Poll, conducted by Selzer & Company, dug deeper into voter intentions by asking respondents a battery of questions about their political activity. Focusing just on likely voters, we found a much narrower lead on the generic House ballot than other polls, but that Democratic voters reported higher levels of political activity than their Republican counterparts.

Sixty-nine percent of our respondents said they would “definitely vote” in the November elections. While Democrats are less likely to turn out than Republicans overall, we found the parties tied in their overall share of the likely electorate. That’s good news for Democrats, who often lose the battle for turnout in midterms. The good news for Republicans is that, among these likely voters, we found only a 2-point advantage on a generic House ballot for Democrats — far less than other polls.

What to make of this? A key finding in our data was the difference between the parties in the level of political activity that likely voters reported. Across the board, Democrats reported engaging in political activity more often than Republicans in the recent past and said that they plan to do more in the near future.

For example, 33 percent of Democrats, compared to 17 percent of Republicans, reported attending a political meeting or rally. Democrats had an 11-point advantage in the percentage of respondents giving money to a candidate, an 18-point advantage in contacting elected officials, and an 11-point advantage in helping someone else register to vote. These margins are of a similar magnitude for the activities Democrats and Republicans expect to take in the near future.

Our findings show an engaged Democratic electorate actively participating in politics at higher levels than their Republican counterparts, consistent with reports nationwide of heavy Democratic turnout in special elections. While the Democratic edge on the generic ballot is smaller than what has been reported elsewhere, the intense political activity of Democratic voters suggests that the party retains a distinct advantage headed into November.

What does this mean for Republicans and Democrats as they prepare for election day? One statistic illustrates the different challenges facing each party. Historically, Republicans are more likely to vote than Democrats in midterm elections. Consistent with that, we found that 86 percent of Republicans say they will definitely vote, versus 70 percent of Democrats. While turnout almost certainly will be lower among both groups on election day, our poll is a good indication of the relative difference between the parties.

The strategic dilemma facing Republicans is that their turnout may have little room to grow, while many Democrats remain to be mobilized. Rallies by President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE, designed to stabilize Republican turnout by keeping his supporters enthusiastic, may have the unintended effect of boosting Democratic turnout, given the president’s unpopularity among Democrats. Republican leaders will need to carefully weigh the pros and cons of embracing a deeply polarizing president in a midterm cycle that is already tilting against them.

If Democrats do take the House in November, they would do well to remember the 1994 elections. President Clinton was deeply unpopular, his signature health care initiative had failed, and Republicans swept to power in Congress in a historic landslide. Most observers assumed Clinton was politically wounded and likely to lose his bid for re-election in 1996. Instead, Clinton regained his popularity by sparring with the Republican Congress and went on to win re-election decisively.

President Trump may find a Democratic House to be similarly to his political advantage. The president excels at political combat, and will benefit from having Democrats on whom to blame his frustrations, rather than a Republican majority. Democrats will find governing with a Republican president and likely Republican Senate to be difficult at best. Within the House, the remaining Republican seats will come from the reddest of red districts, and their members will be little inclined to compromise.

If the past two years have been a challenge, what’s to come may be harder still.

Peter Hanson is associate professor of political science and a specialist in American politics at Grinnell College. His research explores the politics of Congress. He is the author of “Too Weak to Govern: Majority Party Power in the U.S. Senate” (Cambridge 2014).