WASHINGTON — After weeks of arduous negotiations, on April 6, 2006, a bipartisan group of senators burst out of the “President’s Room,” just off the Senate chamber, with a deal on new immigration policy.

As the half-dozen senators — including senators McCain and Kennedy — headed to announce their plan, they met Senator Obama, who made a request common when Capitol Hill news conferences are in the offing: “Hey, guys, can I come along?” And when Mr. Obama went before the microphones, he was generous with his list of senators to congratulate — a list that included himself.

“I want to cite Lindsey Graham, Sam Brownback, Mel Martinez, Ken Salazar, myself, Dick Durbin, Joe Lieberman … who’ve actually had to wake up early to try to hammer this stuff out,” he said.

To Senate staff members, who had been arriving for 7 a.m. negotiating sessions for weeks, it was a galling moment. Those morning sessions had attracted just three to four senators from each side, Senator Specter, a Republican from Pennsylvania, recalled, each deeply involved in the issue. Mr. Obama was not one of them. But in a presidential contest involving three sitting senators, embellishment of legislative records may be an inevitability, Mr. Specter said with a shrug.

Unlike governors, business leaders, or vice presidents, senators — the last to win the presidency was John Kennedy in 1960 — are not executives. They cannot be held to account for the state of their states, their companies, or their administrations. What they do have is the mark they leave on the nation’s laws — and in Mr. Obama’s brief three-year tenure, as well as Senator Clinton’s seven-year hitch, those marks are far from indelible.

“It’s not an unusual matter for senators to take a little extra credit,” Mr. Specter said.

Both Mr. Obama and Mrs. Clinton have tried to make the most of it, and Mrs. Clinton has attempted to bolster her Senate resume with her less-than-transparent track record as first lady. The release Wednesday of more than 11,000 pages of documents from Mrs. Clinton’s years in the White House sent reporters and political opponents scrambling for evidence that might contradict her lofty assessment of her performance in those years.

The Obama campaign pounced on the documents, using them to argue that the senator from New York had understated her role in securing the passage of the North American Free Trade Agreement and overstated her roles in foreign policy decisions and the passage of the Family and Medical Leave Act early in her husband’s administration.

With colleagues in Congress quick to claim credit where it is due, word moves quickly when undue credit is claimed.

“If it happens once or twice, you let it go,” Senator Dodd, a Connecticut Democrat and an Obama supporter, said. “If it becomes the mantra, then you go, ‘Wait a minute.'”

Immigration is a case in point for Mr. Obama, but not the only one. In 2007, after the first comprehensive immigration bill had died, the senators were back at it, and again, Mr. Obama was notably absent, staffers and senators said. At one meeting, three key negotiators recalled, he entered late and raised a number of questions about the bill’s employment verification system. Messrs. Kennedy and Specter both rebuked him, saying that the issue had already been resolved and that he was coming late to the discussion. Mr. Kennedy dressed him down, according to witnesses, and Mr. Obama left shortly thereafter.

“Senator Obama came in late, brought up issues that had been hashed and rehashed,” Mr. Specter recalled. “He didn’t stay long.” Just this week, as the financial markets were roiling in the wake of the Bear Stearns collapse, Mr. Obama made another claim that was greeted with disbelief in some corners of Capitol Hill. On March 13, Mr. Dodd, the chairman of the Senate Banking Committee, and the chairman of the House Financial Services Committee, Rep. Barney Frank, a Democrat from Massachusetts, unveiled legislative proposals to allow the Federal Housing Administration to guarantee new loans from banks willing to help homeowners in or approaching foreclosure. Mr. Obama and Mrs. Clinton were in Washington for a day-long round of budget voting, but neither appeared at the housing news conference.

Yet Mr. Obama on Monday appeared to seek top billing on Mr. Dodd’s proposal.

“At this moment, we must come together and act to address the housing crisis that set this downturn in motion and continues to eat away at the public’s confidence in the market,” Mr. Obama said. “We should pass the legislation I put forward with my colleague Chris Dodd to create meaningful incentives for lenders to buy or refinance existing mortgages so that Americans facing foreclosure can keep their homes.”

Mr. Dodd did say that Mr. Obama supported the bill, as does Mrs. Clinton. But he could not offer pride of authorship to the candidate he wants to see in the White House next year.

“I’ve talked to him about it at some length,” Mr. Dodd said. “When Senator Obama was there for that full day of voting, we had long conversations about it. He had excellent questions and decided to support it.”

Mrs. Clinton also has her share of colleagues only too willing scrutinize her claims. Her campaign Web site describes Mrs. Clinton’s “successful effort to create” the popular State Children’s Health Insurance Program during her husband’s tenure in the White House, and she has placed herself in the middle of major international events, including the Northern Ireland peace process and the Balkan conflict.

But prominent Democratic senators, Irish historians, and even Sinbad the comedian, who accompanied Mrs. Clinton to Kosovo, are challenging some of her assertions.

During months of SCHIP negotiations in 1997, her name rarely surfaced in news accounts. Mrs. Clinton never testified before Congress or held a news conference on the bill.

When Senator Hatch, a Republican from Utah, the lead Republican negotiator of the children’s health bill, heard reports that Mrs. Clinton was depicting herself as SCHIP’s main advocate, “I had to blink a few times,” he said. Mr. Hatch said he doesn’t recall a single conversation with Mrs. Clinton about SCHIP, even a mention of her name. “If she was involved, I didn’t know about it,” he said.

“You know how she says, ‘I started SCHIP’? Well, so did I,” joked Senator Rockefeller, a West Virginia Democrat, one of the Democrats who pushed the bill across the finish line along with Mr. Kennedy. Both have endorsed Mr. Obama.

Some Clinton insiders also are uncomfortable with some of her assertions. “I don’t really like the way she talks about her role in SCHIP,” conceded one former Clinton administration official, who supports the first lady’s candidacy, speaking on the condition of anonymity in order to express his views candidly. “She doesn’t say it right. What she should say is ‘I was the driving force in the administration.’ That’s pretty big, and it’s all true.”

Mr. Obama has left discussion of SCHIP authorship to his allies. But his campaign has launched a broad challenge to Mrs. Clinton’s international bona fides.

In a memo last week, a senior adviser of Mr. Obama, Gregory Craig, President Clinton’s lawyer during his impeachment proceedings, disputed a series of Mrs. Clinton foreign policy claims. “When your entire campaign is based upon a claim of experience, it is important that you have experience to support that claim,” Mr. Craig wrote.

But it may be SCHIP that presents the biggest question marks for her. The issue combines Mrs. Clinton’s twin passions for health care and children’s causes, and Mrs. Clinton talks of it like a proud parent. Speaking to General Motors workers last month, she said: “If you want universal health care, you have to take on the insurance companies — that’s exactly what I did as first lady. And when we weren’t successful, I kept on fighting until we got health care for 6 million children.”

Last fall, Mr. Kennedy said SCHIP “wouldn’t be in existence” without Mrs. Clinton’s support inside the White House. But when her rhetoric on the campaign trail started to filter back to the Capitol, the veteran legislator became stingier with his praise.

“At the last hour, the administration supported it, and she was part of the administration, so I suppose she could say she supported it at the time,” Mr. Kennedy said.

The health policy coordinator in the Clinton White House, Chris Jennings, offers a different account. He recalled discussing an SCHIP-like program with the first lady even as her universal plan was unraveling. Mr. Jennings said Mrs. Clinton pressed her husband to include children’s health coverage in the 1997 State of the Union address and fiscal 1998 budget request.

But context is key, Mr. Jennings added. Barely two years had passed since the collapse of the universal health-care idea, and Mrs. Clinton was still nursing deep political wounds. “She low-keyed her exposure, but that was on purpose,” Mr. Jennings said. “Her feeling was ‘I know my role, I’m going to be quiet, but I’m not going to go away.'”