Tens of millions of dollars will be spent this year in an effort to boost turnout in the November elections. But the longer-term trends suggest that any marginal increase in what is expected to be a low-turnout election won’t have much effect on one of the chronic problems of America’s politics.

The Center for the Study of the American Electorate (CSAE) recently issued a dreary summation about participation in the primary elections so far this year. Based on the 25 states that have already held their primaries, the report chronicled a pattern of voter indifference and, in some cases, record low turnout.

In 15 of the 25 states with statewide primaries, turnout was the lowest ever, and only three of the 25 saw an increase over the last mid-term election in 2010. One of those that produced increased turnout was Mississippi, but that happened during the extraordinarily contested run-off election between Sen. Thad Cochran (R) and his tea party challenger state Sen. Chris McDaniel.

Taken together, just 15 percent of the voting-age population cast ballots — or 18.2 million people out of 122.8 million eligible. Turnout was 17 percentage points lower than the most recent high-water mark of 32 percent in 1966. Democrats were down 14.5 points from their 1970 high, or 20.9 percent of eligible citizens, and Republicans were down five points from their 1966 high of 13 percent.

The figures come at a time of fierce national debate about voting laws — from efforts designed to make it easier to vote to actions in Republican-led states that could make it less easy to vote. But the CSAE report raises questions about the practical effect of such changes as same-day registration, no-fault absentee ballots or voting by mail.

Election Lab: See our current forecast for every congressional race in 2014

Prior research suggested those features have had a positive, though limited, effect on participation. The new report raises questions about those conclusions.

Four of the 25 states that have held primaries so far allow same-day registration. All saw turnout decline between 2010 and 2014. Oregon, which uses mail ballots, saw record-low turnout. California, where two-thirds of voters mail in their ballots, saw the lowest turnout ever.

The results in states that allow in-person early voting or no-excuse absentee voting were no more encouraging. Eight states that have held primaries this year employ both procedures. Two saw turnout increase; six had record lows.

“The numbers in this report reflect how deeply citizens are turning away from political engagement and from positive feelings about one or another major political party,” wrote Curtis Gans, the center’s longtime director.

Elaine Kamarck, a senior fellow at the Brookings Institution, addresses the problem in a newly released article that draws together concerns about the polarized political environment and low turnout in congressional primaries. She analyzes ideas that have been offered for increasing participation in these primaries and, possibly, reducing polarization by lessening the influence of the most ideologically driven voters.

One idea is to assure that all primaries are open to any eligible voter in the state or district. Cochran won his runoff in Mississippi by appealing to Democrats, and especially to African Americans. McDaniel and his tea party supporters cried foul, arguing that party nominations should be decided by party members — in other words, by conducting “closed” primaries.

What happened in the Mississippi runoff was unusual, perhaps an aberration, both in Cochran’s blatant appeal to Democrats and the spike in turnout in the second round of voting. The open primary saved Cochran, but there’s no widespread evidence that open primaries increase turnout or reduce polarization.

California now uses what is known as a blanket primary. Candidates from all parties are on the same ballot and the top two finishers, regardless of party, move on to the general election. The main goal is to reward candidates who can appeal as much to the center of the electorate as to the wings.

It’s too soon to draw any firm conclusions from the California experiment as to whether it produces more moderate candidates, but there have been no dramatic changes so far, while turnout has been dismal.

Another idea aimed at lessening polarization is to create congressional districts that are more competitive in general elections, thereby potentially changing the dynamics of the primaries. The Cook Political Report has analyzed trends dating back two decades. In that time, the number of competitive House districts has declined from 164 to just 90.

Thirteen states, including California, have taken the redistricting process out of the hands of state legislators and given it to an independent commission. Kamarck cites some evidence to suggest that over time this could have a positive effect, but she also notes that this could be undermined by geographical distribution of the population.

Turnout in House primaries is even lower than for statewide offices. With assistance from William Galston of Brookings and Hahrie Han, a political science professor at Wellesley College, Kamarck estimated that turnout in congressional primaries averaged about 5.4 percent of the voting age population in 2002, 4.6 percent in 2006 and 7.5 percent in 2010.

Such low turnout in largely uncompetitive districts gives rise to the potential for more ideological battles in primaries — and this apparently has happened. It’s not that there are significantly more primary challenges taking place — incumbents are still generally safe in both primaries and general elections — but their nature appears to be changing.

Kamarck cites the work of Robert G. Boatright, a political scientist at Clark University and author of “Getting Primaried: The Changing Politics of Congressional Primary Challenges.” In past years, primary challenges usually arose due to scandal or longevity — an incumbent who had served many terms and had lost touch with his or her district.

Today, ideological challenges have become somewhat more common. But the fact that outside groups are now willing to spend money to challenge incumbents in those primaries can change behavior, prompting incumbents to worry about an ideological challenge. That’s especially the case for Republicans.

Kamarck argues that one way around the problem of low turnout in congressional primaries is to limit the days on which those elections are held to one day, or at most just a few. Currently, the primaries are spread out over seven months. In August alone, there will be five different days on which states hold Senate primaries, including a Thursday and a Saturday. Only rarely do congressional primaries draw much media attention, and many voters have no idea that when the primary in their state will be held.

By concentrating the primaries on one or a very few days, there would be more media attention and in effect a national conversation, which in turn could boost participation. But making this happen would be difficult. States control the dates of primaries, and Congress isn’t likely to intervene. The two national parties do coordinate to help establish the dates of most presidential primaries.

Gans argues that the problem of low turnout relates less to election laws and procedures and more to substantive issues.

“The reason should be obvious,” he writes. “The core problem of participation does not reside in the realm of procedure but rather in motivation.”

Between now and November, ask what the candidates and the major parties are doing to motivate people to vote.