For campaign watchers, today’s big news is that after four decades in Congress, Sen. Barbara Mikulski, the dean of women senators, is retiring.

Despite the election of Republican Larry Hogan as governor last fall, Maryland is a very Democratic state. Democrats are strongly favored to retain Mikulski’s seat, so her retirement is unlikely to have much effect on the battle for control of the Senate after 2016.

Yet Mikulski’s decision is still an interesting example of how campaigns have changed. Her announcement comes quite early in the year before the election. Yet the Maryland Democrat is not the first U.S.senator to decline to run for another term. On Jan. 8, Barbara Boxer of California announced that she would be retiring in 2016.

The timing of these announcements means that Boxer and Mikulski will spend the vast majority of the 114th Congress as lame ducks. They also let the campaign to replace them begin very early. In California, Attorney General Kamala Harris announced her Senate bid in January, and already seems well on her way to the Democratic nomination and probably the Senate, given the Golden State’s political leanings.

Why is this all happening so far in advance of the 2016 election, even in states that appear safe for one party? Have senators always announced their retirement so early in the electoral cycle? If not, why have they started doing so?

In a new article, I show that senators have been making such early retirement announcements for about 40 years. It was not always this way. For most of the 20th century, senators waited into their final years of their terms before throwing in the towel. From 1920 (the first campaign in which all senators had been directly elected) through 1972, the median retiring senator announced his departure 260.5 days before the general election and only 99 days before the filing deadline for the primary election. Since the Federal Election Campaign Act (FECA), the median senator has announced her retirement 509 days before the general election and 321.5 days before the filing deadline. What changed?

We need to follow the money, and the laws about the money. Campaign finance law has a lot to do with senators’ early retirement announcements. Congressional campaigns, especially Senate races, are increasingly expensive. However, it is not the cost of campaigns alone that explains these trends. FECA, a statute enacted in 1972 and importantly amended in 1974, plays an important role in encouraging retiring senators to make their intentions clear very early in the campaign cycle.

Two key provisions of FECA help produce the very early retirement announcements we now observe. The first one limits the amount individuals can contribute to a congressional candidate’s campaign. In 2014, this limit was $2,600. This restriction made fundraising much more time-consuming than it used to be. Senators could no longer rely on handful of big donors. Instead, they would need to devote an enormous amount of time to fundraising to collect the millions they needed to be reelected.

The second key aspect of FECA is the quarterly reporting requirement. Senators (and other congressional candidates) must file quarterly reports with the Federal Election Commission detailing their fundraising. These reports are public and give others in the political world a clear picture of how actively a senator is – or is not –  fundraising in the years before their election. When senators are NOT seen raising considerable sums well in advance, observers infer that the senator will probably retire, whatever he or she may say about future plans. Given how little she had banked, Boxer’s announcement in January came as no surprise to California politics watchers.

The public nature of fundraising under FECA means that senators who are thinking about retiring or even planning to do so can no longer conceal their intentions without a lot of effort. To even seem like they are running for reelection they need to spend time raising funds, an activity most do not enjoy. Doing this when they know they are not going to run in the end is not an appealing prospect for senators. So I argue that FECA ”forces the hands” of senators. Once campaigns were not so expensive. Even after television increased the cost of running for office, senators at first could still quietly raise funds quickly from a small group of well-heeled donors. These activities were not as visible either, leaving senators’ intentions more ambiguous in many cases. As a result, they could play their cards close their vests, and did not have to make themselves into lame ducks so early in the process, or set off the jockeying among the contenders to succeed them we are now seeing.

Scholars have found that retiring legislators behave differently, in various ways. They are more likely to miss votes, to go home less often and to introduce and co-sponsor fewer bills. Much of the activity they de-emphasize is symbolic and they are not necessarily neglecting the important parts of their job. There is less agreement about whether retiring legislators start to vote differently, once reelection is no longer a concern. Most of this research has focused on members of the U.S House, who are more numerous. However, representatives generally face less taxing campaigns than senators and do not tend to announce their retirements so far in advance.

Yet while there is more to learn about how retirement affects legislators’ behavior, forcing senators to decide on retirement vs. reelection so early in the cycle does sever the linkages between representative and constituents in ways scholars and political observers have not previously noted. It’s far from clear that this is an entirely positive development. The trend toward early retirement announcements, the rise of lame duck senators and the growth of the permanent campaign were not goals of campaign finance reformers in the 1970s, yet they are consequences of the reforms they helped enact.