The two-party system is not a closed system.
In Missouri, primary elections - and, to a lesser extent, caucuses - are vulnerable to party crashers.
A state senator has offered legislation designed to plug gaps in the primary process. The proposal, if nothing else, shows the difficulties of securing the system.
In our two-party system, members of each major political party - Democrat and Republican - select the party's nominee through a caucus or primary.
At caucuses, like those held Saturday by Republicans, attendees are asked to certify party allegiance. This honor system does not guard against deceitful intruders.
Primaries are even more porous.
Selection of a party's nominee may be - and routinely is - influenced by voters not among the party faithful.
Primary voters are asked their party preference at the polling places.
Independents and unaffiliated voters may select the more interesting, contested races. These voters are identified by the refrain: "I vote for the person, not the party."
In addition, members of one political party have been known to infiltrate the opposing party's primary, in an effort to advance a weaker challenger to the general election.
State Sen. Jay Wasson, R-Nixa, has proposed legislation to tighten party affiliation requirements in primaries.
Under his bill, voters would be required to declare party affiliation when they register to vote. Voters would be permitted to change their affiliation, but would need to do so in advance of the election, not at the polling place on election day.
Under questioning, Wasson admitted the issue of independent voters "is one of the points I'm wrestling with now."
And, asked whether all taxpayers should finance party-specific primaries, Wasson conceded "that's not an unreasonable point."
Further complicating the proposal is the estimated cost provided by the Legislative Research Committee's Oversight Division, which attached a price tag of almost $2.4 million in the 2012-13 business year, and another $26,615 in each of the following two business years.
Although Wasson acknowledges his bill may not make much legislative progress, it raises issues worthy of discussion.
Those issues are at the core of how the people - partisans and independents - act, react and interact in selecting our representatives and leaders.