“Federalism” is the all-purpose word used to describe the complex relationship between the federal government and the states.

As the United States enters an election year in which the role of government is a central issue, federalism is showing signs of strain, especially when it comes to security identification and marijuana use.

The greatest tension between the federal government and the states has been caused by the Homeland Security Department’s renewed determination to enforce the Real ID Act, a 10-year-old law that requires stricter security standards for state driver’s licenses and other identification cards.

In the context of concern about terrorism, fraud and identity theft, Homeland Security is insisting that all states comply with Real ID or risk losing driver’s licenses as a valid means of identification.

Some states have resisted, citing privacy concerns. More than a dozen states have passed laws barring their motor vehicle departments from complying with the law.

If the federal government enforces Real ID, passengers in noncomplying states would no longer be able to use driver’s licenses as identification when boarding commercial aircraft and would have to use passports instead. Only 46 percent of Americans have passports, according to recent data.

“This is a game of intimidation being played out between Congress and the federal government and state governments, with ordinary citizens being squeezed in the middle,” Edward Hasbrouck of The Identity Project, an Oakland-based privacy group, told The New York Times.

A showdown with four noncomplying states was averted, or at least postponed, on Jan. 6 when the DHS gave California, Alaska, New Jersey and South Carolina an extension until Oct. 10.

Minnesota, which has yet to receive an extension, could become the first state in which the federal crackdown in Real ID is tested. State Sen. Warren Limmer, R-Maple Grove, the assistant majority leader, said the federal government was using a “heavy club” in an effort to force state governments into compliance.

Some civil liberty groups opposed to Real ID see the law as a step toward a national identification card. Opponents also cite last year’s theft of millions of private records from the Office of Personnel Management as a sign that the federal government does not maintain secure databases.

Marijuana laws are another arena in which state and federal interests collide. Presently, California and 22 other states permit medical use of marijuana, plus four — Alaska, Colorado, Oregon and Washington — and the District of Columbia that allow so-called recreational use of the drug.

As many as eight states — including California — may consider initiatives in 2016 that would completely legalize marijuana.

Federal law classifies marijuana in the most dangerous category of narcotics, alongside heroin and LSD, which according to the law have no medical benefits.

Congress, however, has twice voted in favor of lifting the federal ban on medical marijuana. The Obama administration has also over time softened its opposition to marijuana use. Veterans who use medical marijuana in states where it is legal have become eligible for veterans benefits. The Drug Enforcement Administration no longer interferes with Native American reservations that choose to grow and sell marijuana.

Supposedly, the Justice Department has stopped targeting medical marijuana businesses as long as they abide by state laws. This policy, however, is enforced inconsistently, according to Americans for Safe Access, a medical marijuana advocacy group. Mike Liszewski, the group’s spokesman, told the Los Angeles Times that “the number of raids has dropped substantially though not completely.”

California, one of the states in which voters this year will decide if marijuana should be fully legalized, has also become pivotal in the complicated legal battle over medical marijuana.

Federal prosecutors have continued to pursue marijuana dispensaries in the Golden State, citing flaws in the original medical marijuana law that allowed unscrupulous distributors to dispense the drug to those without a medical need.

The flaws were real enough. Last year the Legislature passed and Democratic Gov. Jerry Brown signed three measures to correct the defects, but they won’t take effect until 2018.

The long lead time between passage of these measures and the date they become effective has created a legal vacuum that federal prosecutors have attempted to fill by going after major dispensaries. These actions defy a congressional amendment — passed in 2014 and reauthorized in 2015 — that bars the Justice Department from spending money to prevent states “from implementing their own laws” on medical marijuana.

Medical marijuana advocates believed they had achieved a breakthrough last October when U.S. District Judge Charles Breyer issued a ruling that permitted the re-opening of California’s first licensed marijuana dispensary, the Marin Alliance for Medical Marijuana.

The dispensary opened in 1998 and was closed in 2011 by an injunction sought by the Justice Department. Breyer, the brother of U.S. Supreme Court Justice Stephen Breyer, approved the injunction.

But that was before Congress had acted to protect states that permit medical use of marijuana. In his ruling, Breyer implicitly rebuked the Justice Department for ignoring Congress.

“It defies language and logic for the government to argue that it does not prevent California from implementing its medical marijuana laws by shutting down these … heavily regulated marijuana dispensaries,” he said.

Medical marijuana advocates hoped this was the end of the matter, but the Justice Department has announced its intention to appeal this ruling.

A principal target of federal prosecutors in California is Harborside Health Center, a $25-million-a-year Bay Area business that is believed to be the nation’s largest marijuana dispensary.

The center has proved a boon for the perennially cash-strapped City of Oakland, which licenses it and takes a cut of the profits. The Justice Department suspects but hasn’t proven that Harborside sells marijuana to those who use it for recreational purposes.

Like the battle over enforcement of Real ID, the controversy over medical marijuana — indeed, over marijuana use in general — cuts across partisan and ideological lines.

The principal authors of the congressional amendment that protected states with medical marijuana laws are two California lawmakers, liberal Rep. Sam Farr, D-Carmel, and conservative Rep. Dana Rohrabacher, R-Huntington Beach, who rarely agree otherwise.

Last month, this column approvingly cited a famous opinion by Supreme Court Justice Louis Brandeis, who in 1932 opined that states serve as laboratories of democracy and could “if its citizens choose, try novel social and economic experiments without risk to the rest of the country.”

But when it comes to enforcement of marijuana laws and to a lesser extent Real ID, it’s the federal government that seems to be doing the experimenting — and not without risk.

It’s harmful to federalism, to say the least, for a federal agency to ignore the will of Congress and run roughshod over state laws. Such actions also undermine public trust in the federal government, which the Pew Research Center has found is already at a historic low point.

States are not blameless in the federalism narrative. Too often states seek contradictory goals of greater autonomy and more money from the federal government, which inevitably comes with strings and conditions.

This tendency is illustrated by the division between Republican governors and the Republican-controlled Congress on expanding Medicaid under the Patient Protection and Affordable Care Act to cover persons with income up to 138 percent above the poverty level. So far, 10 GOP governors have put aside their opposition to the ACA and accepted the expansion and two others are trying to get their legislatures to go along.

This division is often portrayed as one of ideology, with the governors cast as moderates and the congressional wing of the GOP as conservatives.

It really has more to do with money. The federal government is currently paying 90 percent of the cost of the expansion, in the process helping governors to balance their state budgets.

This dispute is instructive. Some Republicans in Congress have denounced GOP governors who have gone along with their expansion, believing that it undermines their long-term goal of repealing Obamacare.

But the controversy demonstrates one of the enduring strengths of federalism, which is that it encourages governors and state legislators to speak for their constituents rather than just going along with Washington.

Federalism, for all its missteps, is embedded in the American political system. It will survive the tensions caused by the confused enforcement of marijuana laws and the uncertainty of Real ID.

Lou Cannon, a Summerland resident, is a longtime national political writer and acclaimed presidential biographer. His most recent book — co-authored with his son, Carl — is Reagan’s Disciple: George W. Bush’s Troubled Quest for a Presidential Legacy. Cannon also is an editorial adviser to State Net Capitol Journal, which published this column originally. Click here to read previous columns. The opinions expressed are his own.

Lou Cannon, a Summerland resident, is a longtime national political writer and acclaimed presidential biographer. His most recent book — co-authored with his son, Carl — is Reagan’s Disciple: George W. Bush’s Troubled Quest for a Presidential Legacy. Cannon also is an editorial adviser to State Net Capitol Journal, which published this column originally. Click here to read previous columns. The opinions expressed are his own.